1 Line-by-Line Walkthrough
Read each line, peek at the "Easy idea" for a friendly version, then move to the tables.
1
The s-block of the periodic table contains the elements of Group 1 (alkali metals) and Group 2 (alkaline earth metals). Their general valence-shell configuration is ns¹ (Group 1) and ns² (Group 2), where n is the principal quantum number.
Easy ideaThe "s-block" name comes from the outer electrons being in an s-orbital. Just two columns of the table.
2
Group 1 elements are Li, Na, K, Rb, Cs and Fr. Group 2 are Be, Mg, Ca, Sr, Ba and Ra. All are highly reactive metals, never found free in nature; always combined.
Easy ideaThey are too friendly with oxygen and water — they always come with friends.
3
Down each group, atomic and ionic radii increase, ionisation enthalpy decreases, melting and boiling points decrease, and metallic character/reactivity increases.
Easy ideaGoing down: atoms get bigger, electrons further away, easier to give up — so they become more reactive.
4
Hydration enthalpy follows the opposite trend: it is highest for the smallest cation (Li⁺ for Group 1, Be²⁺ for Group 2) and decreases down the group.
Easy ideaSmaller ion ⇒ stronger pull on water molecules ⇒ bigger hydration enthalpy.
5
Alkali metals react with water vigorously, giving the hydroxide and hydrogen: 2M + 2H₂O → 2MOH + H₂. Reactivity with water: Li < Na < K < Rb < Cs.
Easy ideaDrop a tiny bit of Li in water → fizz. Drop Cs → explosion. Bigger atom, easier to give up electron.
6
Reaction with oxygen: Li gives the monoxide (Li₂O); Na gives mostly peroxide (Na₂O₂); K, Rb, Cs give superoxides (MO₂). The size of M⁺ controls which oxide ion (O²⁻ / O₂²⁻ / O₂⁻) is stabilised.
Easy ideaSmall Li⁺ pairs only with the small O²⁻. Bigger cations stabilise bigger oxide ions.
7
Each alkali metal shows a characteristic flame colour: Li → crimson, Na → golden yellow, K → violet, Rb → red, Cs → blue. The valence electron is excited then emits visible light when returning.
Easy ideaA "fingerprint" colour for each alkali metal in fire.
8
Alkali metals dissolve in liquid ammonia to give blue, paramagnetic, conducting solutions due to ammoniated electrons (e⁻·NH₃). At higher concentration these turn bronze/copper coloured and even more conducting.
Easy ideaThe "freed" electrons swim around in ammonia and make it blue.
9
Anomalous behaviour of Li: very small ion, high polarising power, high lattice energy. Li shows similarities with Mg (diagonal relationship) — covalent character of LiX, formation of nitride Li₃N, decomposition of carbonate.
Easy ideaLi is the "odd one out" of Group 1 — it behaves like a Group 2 element diagonally placed (Mg).
10
Important Na compounds: NaCl (common salt), NaOH (caustic soda, from chlor-alkali process), Na₂CO₃ (washing soda, Solvay process), NaHCO₃ (baking soda, antacid).
Easy ideaThe four sodium compounds you must memorise — every NEET asks at least one.
11
In Group 2, ionisation enthalpy is higher than the corresponding alkali metal because of the extra electron in the same shell — second IE is needed to form M²⁺. Despite needing two electrons, group 2 hydration enthalpies are large enough to make them reactive in solution.
Easy ideaTwo electrons cost more, but Group 2's small, highly-charged cations are happy in water.
12
Anomalous behaviour of Be: very small size, high polarising power, exceptionally high charge/radius ratio. Be forms covalent compounds (BeCl₂ is linear and polymeric), shows amphoteric hydroxide, and exhibits a diagonal relationship with Al.
Easy ideaBe is so small and pulls so hard on electrons that its compounds look covalent — like an Al cousin.
13
Group 2 reactivity with water: Be does not react; Mg reacts only with hot water/steam; Ca, Sr, Ba react readily with cold water giving hydroxide + H₂.
Easy ideaSmaller group 2 elements are shy with water; the larger ones love it.
14
Important Ca compounds: CaO (quick lime, from heating limestone), Ca(OH)₂ (slaked lime), CaCO₃ (limestone, marble, chalk), CaSO₄·2H₂O (gypsum), CaSO₄·½H₂O (plaster of Paris), CaCl₂ (desiccant).
Easy ideaCalcium is the building-block element — bricks, cement, plaster, even your bones.
15
Biological importance: Na⁺ and K⁺ regulate nerve impulses, fluid balance; Ca²⁺ is central to bones, teeth, blood clotting, muscle contraction; Mg²⁺ is a cofactor for many enzymes and a key ion in chlorophyll.
Easy ideaThese ions are not just inorganic — they keep your body running.
2 Concepts to know for NEET MCQs
| Concept | Key idea | NEET focus |
|---|---|---|
| Periodic trends | Radius ↑, IE ↓, M.P./B.P. ↓, reactivity ↑ down a group | "Order of IE / radius / reactivity" MCQs |
| Hydration enthalpy | Smallest ion ⇒ highest ΔHhyd | "Which has highest hydration enthalpy?" |
| Flame colours | Li-crimson, Na-golden, K-violet, Rb-red, Cs-blue; Ca-brick red, Sr-crimson, Ba-apple green | Direct memory recall |
| Anomalous behaviour | Li anomalous in Gp 1; Be anomalous in Gp 2 | Reason behind anomaly |
| Diagonal relationship | Li↔Mg, Be↔Al, B↔Si | Why? Charge/radius ratio similarity |
| Oxide types | Li → Li₂O (monoxide); Na → Na₂O₂ (peroxide); K, Rb, Cs → MO₂ (superoxide) | "Which metal forms peroxide / superoxide?" |
| Reducing power | In aqueous solution: Li is strongest reducer (very negative E°) | Counter-intuitive — IE is highest but E° most negative |
| Solvay process | NaCl + NH₃ + CO₂ + H₂O → Na₂CO₃ | Industrial preparation of washing soda |
| Important Na compounds | NaCl, NaOH, Na₂CO₃, NaHCO₃ | Common names & uses |
| Important Ca compounds | CaO, Ca(OH)₂, CaCO₃, gypsum, POP, CaCl₂ | Formulae, names, uses |
| Hardness of water | Temporary (bicarbonates) vs permanent (Cl⁻, SO₄²⁻) | "How is hardness removed?" |
| Solubility trends | Group 2: sulphate solubility ↓; hydroxide solubility ↑ down the group | Easy to confuse — memorise both |
3 Important reactions & formulas
| Reaction / Compound | Equation / Formula | Notes |
|---|---|---|
| Alkali metals with water | 2M + 2H₂O → 2MOH + H₂↑ | Reactivity: Li < Na < K < Rb < Cs |
| Li + O₂ | 4Li + O₂ → 2Li₂O | Only monoxide |
| Na + O₂ | 2Na + O₂ → Na₂O₂ | Peroxide formed |
| K, Rb, Cs + O₂ | M + O₂ → MO₂ | Superoxide |
| Group 2 metals with O₂ | 2M + O₂ → 2MO | Mostly monoxides (Ba can give peroxide BaO₂) |
| Be with steam | No reaction | Anomalous behaviour |
| Mg with steam | Mg + H₂O → MgO + H₂↑ | Only on heating |
| Solvay (Na₂CO₃) | NaCl + NH₃ + CO₂ + H₂O → NaHCO₃ + NH₄Cl2NaHCO₃ ⟶^Δ Na₂CO₃ + H₂O + CO₂ | Industrial soda ash production |
| Chlor-alkali (NaOH) | 2NaCl + 2H₂O → 2NaOH + Cl₂↑ + H₂↑ | Electrolysis of brine |
| Quick lime preparation | CaCO₃ ⟶^Δ CaO + CO₂ | ~1100 °C in kilns |
| Slaking | CaO + H₂O → Ca(OH)₂ + heat | Exothermic; "slaking" of lime |
| Gypsum → POP | CaSO₄·2H₂O ⟶120°C CaSO₄·½H₂O + 1.5 H₂O | Plaster of Paris formation |
| POP setting | CaSO₄·½H₂O + 1.5 H₂O → CaSO₄·2H₂O | Sets back to gypsum on adding water |
| Calcium carbide hydrolysis | CaC₂ + 2H₂O → Ca(OH)₂ + C₂H₂↑ | Source of acetylene |
| Hydration enthalpy trend | ΔHhyd ∝ z²/r | Higher charge or smaller radius ⇒ higher ΔHhyd |
| Polarising power | p ∝ z/r² | Higher for Li⁺, Be²⁺ ⇒ more covalent character (Fajans' rules) |
4 Facts you must remember
| Fact | Why it matters for NEET |
|---|---|
| Alkali metals are soft and can be cut with a knife (Cs is liquid near room temperature) | "Which is the softest / lowest melting alkali metal?" |
| Stored under kerosene (Na, K, etc.) | To prevent reaction with air and water |
| Li is the only alkali metal to form a nitride (Li₃N) by direct combination with N₂ | Anomalous Li behaviour |
| Be(OH)₂ is amphoteric; other Group 2 hydroxides are basic | Be anomalous behaviour |
| BeCl₂ is covalent (polymeric chain in solid, linear monomer in vapour) | Distinguishes Be from rest of Group 2 |
| Group 2 oxides are basic; BeO is amphoteric | Be exception again |
| Li is the strongest reducer in aqueous solution despite highest IE in group | Hydration enthalpy controls E° in water |
| The Solvay process cannot be used to prepare K₂CO₃ | KHCO₃ is too soluble — won't precipitate |
| Lithium carbonate decomposes; Na₂CO₃, K₂CO₃ are thermally stable | Carbonate stability trend |
| Magnesium burns with a brilliant white flame | Common photography flash question |
| Mg²⁺ is at the centre of chlorophyll; Ca²⁺ in bones; Na⁺/K⁺ in nerves | Biological importance MCQs |
| Plaster of Paris (POP) is CaSO₄·½H₂O and sets to give gypsum | Common formula MCQ |
5 Controversial / Confusing Points
| Confusion | Clarification |
|---|---|
| "Why is Li the strongest reducing agent if it has the highest IE?" | E° in aqueous solution depends on three steps: sublimation, ionisation and hydration. Li's very high hydration enthalpy overcomes its high IE ⇒ most negative E°. |
| "Solubility of group 2 sulphates decreases but hydroxides increases. Why?" | Lattice and hydration both decrease down the group, but at different rates. Sulphates: lattice decreases slowly, hydration drops fast ⇒ less soluble. Hydroxides: lattice drops fast ⇒ more soluble. |
| "Be is in Group 2 but behaves like Group 13 Al?" | Be²⁺ and Al³⁺ have comparable charge/radius ratio (~6) ⇒ similar polarising power ⇒ similar chemistry. This is the diagonal relationship. |
| "Order of basicity?" | Among alkali hydroxides, basicity increases down: LiOH < NaOH < KOH < RbOH < CsOH. Same trend in Group 2: Be(OH)₂ < Mg(OH)₂ < Ca(OH)₂ < Sr(OH)₂ < Ba(OH)₂. |
| "Anomalous because of size — same reason for Li and Be?" | Yes. Small size + high polarising power explains anomalous behaviour of both Li and Be. |
| "Carbonate stability down the group?" | Stability increases. Larger cation distorts CO₃²⁻ less ⇒ less likely to decompose. |
| "What's the difference between baking soda and washing soda?" | Baking soda = NaHCO₃ (sodium bicarbonate, mild). Washing soda = Na₂CO₃·10H₂O (sodium carbonate decahydrate, strong base). |
6 Assumptions in this chapter
| Assumption | When it's invoked |
|---|---|
| Periodic trends are assumed to be smooth and monotonic | Discussion of IE, radius, density trends |
| Bonding is purely ionic for most s-block compounds | To rationalise simple formulae like NaCl, CaO |
| Reactivity is governed mainly by ease of losing valence electrons | Justifies the down-group reactivity increase |
| Lattice and hydration enthalpies are the only major factors in solubility | Used to explain Group 2 sulphate / hydroxide trends |
| Flame colour arises only from electronic transitions | Ignores subtle solid-state effects in observed colour intensity |
| Solvay process is used for both Na₂CO₃ and K₂CO₃ | False — assumption breaks for K because KHCO₃ is too soluble |
| Group 2 metals always lose 2 electrons | Be can show some covalent (sharing) behaviour |
7 Exceptions to remember
| General rule | Exception |
|---|---|
| Alkali metals form peroxides / superoxides with O₂ | Li forms only monoxide Li₂O — small Li⁺ cannot stabilise larger O₂²⁻ / O₂⁻ |
| Alkali halides have ionic character | LiCl and LiBr show covalent character (Fajans' rules) |
| Alkali nitrates decompose to nitrite | LiNO₃ decomposes to Li₂O + NO₂ + O₂ (like Group 2) |
| Group 1 reacts with N₂ only at very high T | Li reacts with N₂ at room temperature to give Li₃N |
| Group 2 hydroxides are basic | Be(OH)₂ is amphoteric |
| Group 2 chlorides are ionic | BeCl₂ is covalent and polymeric |
| Group 2 metals react with water to give H₂ | Be does not react; Mg only with hot water / steam |
| Solvay process is general | K₂CO₃ cannot be made via Solvay — KHCO₃ is too soluble |
| Carbonates are stable | Li₂CO₃ decomposes on moderate heating |
| Alkali metals impart flame colour | Be and Mg do not impart any flame colour (Group 2 exception) |
8 Scientists and years
| Scientist | Year | Contribution |
|---|---|---|
| Humphry Davy | 1807–1808 | Isolated K, Na, Ca, Sr, Ba, Mg by electrolysis of molten compounds |
| Johan August Arfwedson | 1817 | Discovered lithium in petalite |
| Robert Bunsen & Gustav Kirchhoff | 1860–1861 | Discovered caesium (1860) and rubidium (1861) using flame spectroscopy |
| Marguerite Perey | 1939 | Discovered francium, last natural alkali metal |
| Louis Nicolas Vauquelin | 1798 | Discovered beryllium in beryl |
| Joseph Black | 1755 | Recognised "fixed air" (CO₂) liberated from magnesia & lime |
| Ernest Solvay | 1861 | Developed the ammonia–soda (Solvay) process for Na₂CO₃ |
| Walter Hermann Nernst | 1888 | Standard electrode potentials and electrochemistry framework |
9 NEET traps to avoid
| Trap | How to avoid it |
|---|---|
| Saying "Li has lowest E° because of lowest IE" | Li has the highest IE in Group 1, yet most negative E° in aqueous solution because of very high hydration enthalpy. |
| Confusing Solvay product | Solvay yields Na₂CO₃ (not NaOH or NaHCO₃ directly); NaHCO₃ is an intermediate. |
| Forgetting that K₂CO₃ cannot be made by Solvay | Because KHCO₃ is too soluble. |
| Confusing baking soda vs washing soda | Baking = NaHCO₃; washing = Na₂CO₃·10H₂O. |
| Wrong oxide assignment | Li→Li₂O; Na→Na₂O₂; K, Rb, Cs→MO₂ (superoxide). |
| Confusing solubility trends in Group 2 | Sulphates ↓, hydroxides ↑ down the group. |
| Mixing up POP and gypsum | POP = CaSO₄·½H₂O (hemihydrate); gypsum = CaSO₄·2H₂O (dihydrate). POP "sets" by reverting to gypsum. |
| Forgetting Be(OH)₂ is amphoteric | Other Group 2 hydroxides are basic. |
| Assuming Be and Mg give flame colour | They don't. Electrons too tightly bound. |
| Saying all alkali halides are 100% ionic | LiCl, LiBr, LiI show appreciable covalent character. |
📊 Diagrams
a) Position of the s-block in the periodic table
Group 1 (ns¹) on the far left and Group 2 (ns²) next to it form the s-block.
b) Diagonal relationships
Li–Mg, Be–Al and B–Si share similar chemistry because of comparable charge/radius ratios.
c) Flame colours summary
Memorise these — direct flame-colour MCQs are almost guaranteed.
d) Periodic trends in alkali metals
Down the group: atomic radius ↑; melting point and ionisation enthalpy ↓.
e) Solvay process flow chart
Ammonia and CO₂ react with brine to precipitate NaHCO₃, which is then heated to give Na₂CO₃.
f) Hardness of water
Temporary hardness from bicarbonates; permanent hardness from chlorides and sulphates.
📝 50 PYQs — 25 NEET + 25 JEE Main
Each card shows Easy idea, Given, To find, Formula and clean Solution. Tap to expand.
Q1NEET 2020The correct order of ionisation enthalpy of alkali metals is
ALi > Na > K > Rb > Cs
BCs > Rb > K > Na > Li
CNa > Li > K > Rb > Cs
DLi > Na > Cs > Rb > K
Easy idea
Atoms get bigger as we go down the group. Bigger atoms hold their outer electron more loosely, so less energy is needed to pull it off.
Given
Down the group, atomic size increases and outer electron is held less tightly.
To find
Order of ionisation enthalpy (IE).
Formula
IE ∝ 1/atomic radius (down a group).
Solution
Atomic radius increases down the group ⇒ IE decreases. Order: Li > Na > K > Rb > Cs.
Answer
(A)
Q2NEET 2019Which of the following gives a crimson red flame test?
ALi
BNa
CK
DRb
Easy idea
Each alkali metal shows its own colour in a flame — like a fingerprint. Lithium glows crimson.
Given
Each alkali metal has a characteristic flame colour due to electron excitation.
To find
Element that gives crimson red flame.
Formula
Flame colour memory: Li-crimson, Na-golden, K-violet, Rb-red, Cs-blue.
Solution
Lithium gives a crimson red flame.
Answer
(A)
Q3NEET 2018The most abundant alkali metal in Earth's crust is
ALi
BNa
CK
DRb
Easy idea
Alkali metals are reactive, so they're locked up in compounds like rock salt. Of those, sodium compounds are everywhere in the crust.
Given
Abundance of alkali metals on Earth.
To find
Most abundant alkali metal.
Formula
Standard geochemical fact.
Solution
Sodium (Na) is the most abundant alkali metal in Earth's crust (~2.27%).
Answer
(B)
Q4NEET 2022Which alkaline earth metal compound is used as a desiccant?
AMgCO3
BCaCO3
CCaCl2
DBaSO4
Easy idea
A desiccant is a moisture sponge. Anhydrous CaCl₂ grabs water vapour very effectively.
Given
Desiccants absorb water vapour to keep substances dry.
To find
Compound used as a desiccant.
Formula
Anhydrous CaCl2 is hygroscopic.
Solution
Anhydrous CaCl2 readily absorbs moisture and is widely used as a desiccant.
Answer
(C)
Q5NEET 2021Plaster of Paris is
ACaSO4·2H2O
BCaSO4·½H2O
CCaSO4
DCa(OH)2
Easy idea
Plaster of Paris is gypsum that has lost most (but not all) of its water — it keeps half a water molecule per formula unit.
Given
Plaster of Paris is the hemihydrate of calcium sulphate.
To find
Chemical formula of Plaster of Paris.
Formula
Heating gypsum (CaSO4·2H2O) at 120 °C gives CaSO4·½H2O.
Solution
Plaster of Paris = CaSO4·½H2O (hemihydrate, also written as 2CaSO4·H2O).
Answer
(B)
Q6NEET 2017The element which gives a golden yellow flame test is
ALi
BNa
CK
DCs
Easy idea
Street sodium-vapour lamps are the same colour. Sodium burns with a familiar golden-yellow flame.
Given
Characteristic flame colours of alkali metals.
To find
Element with golden yellow flame.
Formula
Standard NEET memory list.
Solution
Sodium (Na) gives a golden yellow flame, used in street sodium-vapour lamps.
Answer
(B)
Q7NEET 2020Which alkali metal does NOT form a stable peroxide?
ALi
BNa
CK
DCs
Easy idea
Li⁺ is too small to hold a big peroxide ion stable. So lithium gives only the simple monoxide Li₂O.
Given
Alkali metals react with oxygen to form different oxides: Li forms monoxide; Na forms peroxide; K, Rb, Cs form superoxides.
To find
Alkali metal that does not form a stable peroxide.
Formula
Size effect on lattice energy.
Solution
Lithium forms only the monoxide (Li2O) — small Li+ cannot stabilise the larger peroxide ion.
Answer
(A)
Q8NEET 2019Which of the following has the lowest melting point?
ALi
BNa
CK
DCs
Easy idea
Melting points fall down Group 1 because the metallic bond weakens. Cs has the lowest — almost melts in your hand.
Given
Melting points of alkali metals decrease down the group.
To find
Alkali metal with lowest melting point.
Formula
M.P. ∝ binding strength; weaker metallic bond down the group.
Solution
Cs has the lowest M.P. (~28.5 °C) — melts in the hand.
Answer
(D)
Q9NEET 2018Among the following compounds, which is the most soluble in water?
ABeSO4
BMgSO4
CCaSO4
DBaSO4
Easy idea
Be²⁺ is tiny and grabs water molecules tightly. That huge hydration energy dissolves BeSO₄ better than the others.
Given
Solubility of group 2 sulphates decreases down the group.
To find
Most soluble sulphate.
Formula
Hydration enthalpy decreases faster than lattice enthalpy for larger cations.
Solution
BeSO4 is the most soluble (small Be2+ has very high hydration enthalpy).
Answer
(A)
Q10NEET 2021Which oxide of sodium is the only one that does NOT exist as a free salt?
ANa2O
BNa2O2
CNaO2
DNaO3
Easy idea
Sodium does form Na₂O (monoxide), Na₂O₂ (peroxide), and NaO₂ (superoxide). But NaO₃ (ozonide) is not a stable salt.
Given
Sodium forms monoxide (Na2O), peroxide (Na2O2) and superoxide (NaO2, though small Na+ destabilises).
To find
Sodium oxide that does NOT exist.
Formula
Ozonide NaO3 is not stable for sodium.
Solution
Na ozonide (NaO3) does not exist as a free salt; the rest are real.
Answer
(D)
Q11NEET 2017Which one of the following has the highest hydration enthalpy?
ALi+
BNa+
CK+
DCs+
Easy idea
Hydration enthalpy depends on charge density (charge ÷ size). Li⁺ is the smallest, so it pulls hardest on water molecules.
Given
Hydration enthalpy depends on charge density of cation.
To find
Ion with highest hydration enthalpy.
Formula
Smaller cation ⇒ higher charge density ⇒ stronger water binding.
Solution
Li+ is the smallest, so it has the highest hydration enthalpy.
Answer
(A)
Q12NEET 2022The diagonal relationship of Li is with
ABe
BMg
CAl
DSi
Easy idea
Diagonal pairs: Li-Mg, Be-Al, B-Si. Each pair has a similar charge-to-size ratio.
Given
Diagonal relationship: similarities between an element and the element diagonally placed in the next group.
To find
Element diagonally related to Li.
Formula
Diagonal pairs: Li-Mg, Be-Al, B-Si.
Solution
Li (Group 1, Period 2) is diagonally related to Mg (Group 2, Period 3).
Answer
(B)
Q13NEET 2018Sodium carbonate is also known as
ABaking soda
BWashing soda
CCaustic soda
DSoda lime
Easy idea
Washing soda is the same Na₂CO₃ but with 10 water molecules attached (Na₂CO₃·10H₂O).
Given
Common names of sodium compounds.
To find
Common name of Na2CO3·10H2O.
Formula
Na2CO3·10H2O is widely used in laundry.
Solution
Sodium carbonate decahydrate (Na2CO3·10H2O) is called washing soda.
Answer
(B)
Q14NEET 2020Which one is the strongest base?
ALiOH
BNaOH
CKOH
DCsOH
Easy idea
As cations get bigger, the M–OH bond gets weaker and OH⁻ is released more easily, making the base stronger.
Given
Basic strength of alkali hydroxides increases down the group.
To find
Strongest hydroxide.
Formula
Larger cation ⇒ weaker M–OH bond ⇒ easier OH- release.
Solution
CsOH is the strongest base; LiOH the weakest.
Answer
(D)
Q15NEET 2019The hydrolysis of CaC2 produces
AMethane
BEthylene
CAcetylene
DEthane
Easy idea
Calcium carbide + water gives acetylene gas — the same gas used in old miners' lamps.
Given
Calcium carbide reacts with water.
To find
Gas produced when CaC2 reacts with water.
Formula
CaC2 + 2H2O → Ca(OH)2 + C2H2.
Solution
Acetylene (C2H2) is produced.
Answer
(C)
Q16NEET 2018Quick lime is
ACa(OH)2
BCaO
CCaCO3
DCaSO4
Easy idea
Quick lime is what you get by heating limestone (CaCO₃) — it loses CO₂ to give CaO.
Given
Common names of calcium compounds.
To find
Quick lime.
Formula
Standard nomenclature.
Solution
Quick lime = CaO. Slaked lime = Ca(OH)2. Limestone = CaCO3.
Answer
(B)
Q17NEET 2021Which of the following does NOT form a stable carbonate?
ALi
BNa
CK
DCs
Easy idea
Li⁺ is too small and polarising — it pulls the CO₃²⁻ apart, so Li₂CO₃ decomposes when heated.
Given
Stability of alkali carbonates increases down the group.
To find
Alkali metal whose carbonate is unstable.
Formula
Small Li+ cannot stabilise large CO32-.
Solution
Li2CO3 decomposes on moderate heating to Li2O + CO2; the others are quite stable.
Answer
(A)
Q18NEET 2017Which solution is used in fire extinguishers?
ANaHCO3
BNa2CO3
CNaOH
DNa2SO4
Easy idea
Sodium bicarbonate releases CO₂ when it meets acid, and CO₂ smothers flames by cutting off oxygen.
Given
Reaction of NaHCO3 with acid produces CO2.
To find
Compound used in fire extinguishers.
Formula
Na fire extinguishers release CO2 to smother flames.
Solution
Sodium bicarbonate (NaHCO3) reacts with acid to release CO2, used in foam-type extinguishers.
Answer
(A)
Q19NEET 2020Solvay process is used for the manufacture of
ANaOH
BNa2CO3
CNaHCO3
DNa2O
Easy idea
The Solvay process uses ammonia, brine and CO₂ to make sodium carbonate (washing soda).
Given
Industrial process for sodium carbonate.
To find
Product of the Solvay process.
Formula
Standard NEET fact.
Solution
The Solvay (ammonia–soda) process makes Na2CO3 from NaCl, NH3 and CO2.
Answer
(B)
Q20NEET 2022Which alkali metal forms only a normal oxide on reaction with O2?
ALi
BNa
CK
DRb
Easy idea
Lithium is again unique — it forms only the normal monoxide. Sodium prefers peroxide, the rest prefer superoxide.
Given
Reaction of alkali metals with excess oxygen.
To find
Alkali metal forming only the normal oxide.
Formula
Li2O — only Li forms primarily this; Na→Na2O2; K, Rb, Cs → MO2.
Solution
Li reacts with O2 to give mainly Li2O (a normal oxide).
Answer
(A)
Q21NEET 2018Which is the largest alkali metal cation?
ALi+
BNa+
CK+
DCs+
Easy idea
Ions get larger as we go down a group. Cs⁺ sits at the bottom of Group 1, so it's the biggest cation.
Given
Atomic and ionic radii increase down a group.
To find
Largest M+ cation.
Formula
Standard trend.
Solution
Cs+ is the largest alkali metal cation.
Answer
(D)
Q22NEET 2019Which of these does NOT belong to the s-block?
ANa
BMg
CAl
DCa
Easy idea
The s-block has Group 1 and Group 2 only. Aluminium is in Group 13, the p-block.
Given
s-block contains group 1 and group 2 elements only.
To find
Element NOT in the s-block.
Formula
Al is group 13 (p-block).
Solution
Aluminium (Al) is a p-block element; the others are s-block.
Answer
(C)
Q23NEET 2021Calcium reacts with water
ALess vigorously than Mg
BSame as Mg
CMore vigorously than Mg
DDoes not react
Easy idea
Reactivity of Group 2 metals with water grows down the group: Be < Mg < Ca < Sr < Ba.
Given
Reactivity with water increases down group 2.
To find
Reactivity of Ca with water.
Formula
Standard trend in group 2.
Solution
Ca reacts with cold water more readily than Mg (Mg reacts only with hot water/steam).
Answer
(C)
Q24NEET 2020Which alkaline earth metal does NOT impart any colour to the flame?
ABe
BMg
CCa
DSr
Easy idea
Be and Mg hold their outer electrons too tightly — the energy of excitation falls outside visible range, so no flame colour.
Given
Some alkaline earth metals impart characteristic flame colours.
To find
Element giving no flame colour.
Formula
Be and Mg do not impart flame colour (electrons tightly bound).
Solution
Be (and Mg) do not give a flame colour.
Answer
(A)
Q25NEET 2017The compound mainly responsible for permanent hardness of water is
ACa(HCO3)2
BMg(HCO3)2
CCaSO4
DNaCl
Easy idea
Temporary hardness comes from bicarbonates; permanent hardness comes from sulphates and chlorides of Ca and Mg.
Given
Permanent hardness is from chlorides and sulphates of Ca/Mg.
To find
Cause of permanent hardness.
Formula
Permanent vs temporary hardness.
Solution
CaSO4 (and MgSO4, CaCl2, MgCl2) cause permanent hardness; bicarbonates cause temporary hardness.
Answer
(C)
Q26JEE Main 2019Which of the following is the most thermally stable?
ALi2CO3
BNa2CO3
CK2CO3
DCs2CO3
Easy idea
Bigger cation means less distortion of the CO₃²⁻, so the carbonate doesn't fall apart easily on heating.
Given
Stability of alkali carbonates increases down the group.
To find
Most thermally stable alkali carbonate.
Formula
Larger cation ⇒ less polarising ⇒ more stable carbonate.
Solution
Cs2CO3 is the most thermally stable; Li2CO3 the least.
Answer
(D)
Q27JEE Main 2020The correct order of solubility of group 2 hydroxides in water is
ABe(OH)2 < Mg(OH)2 < Ca(OH)2 < Ba(OH)2
BBa(OH)2 < Ca(OH)2 < Mg(OH)2 < Be(OH)2
CMg(OH)2 < Be(OH)2 < Ca(OH)2 < Ba(OH)2
DAll equally soluble
Easy idea
Group 2 hydroxides get more soluble down the group because their lattice energy drops faster than hydration energy.
Given
Solubility of group 2 hydroxides increases down the group.
To find
Order of solubility.
Formula
Lattice enthalpy decreases faster than hydration enthalpy down the group for hydroxides.
Solution
Be(OH)2 < Mg(OH)2 < Ca(OH)2 < Sr(OH)2 < Ba(OH)2.
Answer
(A)
Q28JEE Main 2018Which is the strongest reducing agent in aqueous solution?
ALi
BNa
CK
DCs
Easy idea
Even though Li has the highest IE, its tiny ion is hugged super-hard by water — that hydration drop makes E° most negative.
Given
Reducing power in aqueous solution depends on standard electrode potential, which depends on ionisation enthalpy, sublimation enthalpy and hydration enthalpy.
To find
Strongest reducing agent in aqueous solution.
Formula
Despite higher IE, Li+ has the most negative E° due to its very high hydration enthalpy.
Solution
Li is the strongest reducing agent in aqueous solution (E°(Li+/Li) = −3.04 V).
Answer
(A)
Q29JEE Main 2021Anomalous behaviour of Li is mainly due to
ASmall size and high polarising power
BLarge size
CHighest reactivity
DLowest IE
Easy idea
Lithium's small size + high charge density makes it behave differently from the rest of Group 1.
Given
Why Li shows anomalous properties.
To find
Reason for anomalous behaviour of Li.
Formula
Combination of small size + high charge density.
Solution
Small atomic/ionic size and high polarising power make Li behave differently — covalent character, lithium-only oxide, etc.
Answer
(A)
Q30JEE Main 2019Diagonal relationship between Be and Al is due to
ASame group
BSimilar size and charge/radius ratio
CSame period
DSame valence electrons
Easy idea
Be²⁺ and Al³⁺ have nearly the same charge ÷ radius ratio (~6), so they polarise like each other.
Given
Why Be and Al show similar properties.
To find
Reason for Be–Al diagonal relationship.
Formula
Comparable size and ionic potential.
Solution
Be2+ and Al3+ have similar charge-to-radius ratio (~6) ⇒ similar polarising power and similar chemistry.
Answer
(B)
Q31JEE Main 2020The colour given by Sr in flame test is
AGreen
BCrimson
CRed
DBrick red
Easy idea
Strontium fires are red-pink (crimson) — used in road flares and fireworks.
Given
Flame colours of alkaline earth metals: Ca-brick red, Sr-crimson, Ba-apple green.
To find
Sr flame colour.
Formula
Memorise standard list.
Solution
Sr gives a crimson (or scarlet) flame colour.
Answer
(B)
Q32JEE Main 2017Which of the following is the strongest base?
ABe(OH)2
BMg(OH)2
CCa(OH)2
DBa(OH)2
Easy idea
Same trend as Group 1: bigger cation → weaker M–OH bond → stronger base. Ba(OH)₂ is the strongest.
Given
Basicity of group 2 hydroxides increases down the group.
To find
Strongest hydroxide.
Formula
Larger ions ⇒ weaker M–OH ⇒ more basic.
Solution
Ba(OH)2 is the strongest base; Be(OH)2 is amphoteric.
Answer
(D)
Q33JEE Main 2022Which Group 2 element is used in flares, fireworks for crimson colour?
ABe
BMg
CCa
DSr
Easy idea
Strontium gives the most intense crimson flame — that's why it's the go-to for red fireworks.
Given
Strontium salts produce intense crimson flames.
To find
Element used for crimson fireworks.
Formula
Application of flame colour.
Solution
Strontium salts (SrCO3, SrCl2) give crimson/scarlet colour, used in flares and fireworks.
Answer
(D)
Q34JEE Main 2018Limestone, marble and chalk are forms of
ACaCO3
BCa(OH)2
CCaSO4
DMgCO3
Easy idea
Limestone, marble and chalk are all CaCO₃ — different crystal habits and impurities.
Given
Natural occurrences of calcium carbonate.
To find
Form of CaCO3.
Formula
Standard NEET/JEE fact.
Solution
All three (limestone, marble, chalk) are forms of CaCO3.
Answer
(A)
Q35JEE Main 2021The compound used as antacid is
ANaHCO3
BNa2CO3
CNaOH
DMg(OH)2
Easy idea
Antacids neutralise stomach acid. Baking soda (NaHCO₃) is mild and edible — perfect.
Given
Antacids neutralise stomach acid.
To find
Compound used as antacid.
Formula
Medicinal sodium bicarbonate is mild and edible.
Solution
NaHCO3 (baking soda) is used as an antacid. Mg(OH)2 (milk of magnesia) is also used.
Answer
(A)
Q36JEE Main 2020Na metal is stored under
AWater
BKerosene
CAlcohol
DAir
Easy idea
Sodium reacts violently with water and oxidises in air. Kerosene keeps both away.
Given
Reactivity of Na with water and air.
To find
Storage medium for Na.
Formula
Na reacts violently with water and oxidises in air.
Solution
Sodium is stored under kerosene to prevent contact with moisture and oxygen.
Answer
(B)
Q37JEE Main 2019Which of the following has zero dipole moment?
ABeCl2
BNaCl
CMgCl2
DKCl
Easy idea
Be is small, so BeCl₂ is covalent and linear — the two Cl pulls cancel out, giving zero net dipole.
Given
BeCl2 is linear, covalent, symmetric molecule.
To find
Compound with zero dipole moment.
Formula
Symmetric linear geometry cancels dipoles.
Solution
BeCl2 is linear (sp hybridised Be) ⇒ zero net dipole. The others are ionic with separated charges.
Answer
(A)
Q38JEE Main 2022The pH of a saturated solution of Ca(OH)2 is approximately
A7
B9
C12
D14
Easy idea
Ca(OH)₂ is sparingly soluble, but the bit that dissolves makes a strongly basic solution — pH around 12.
Given
Ca(OH)2 is sparingly soluble; saturated solution is moderately basic.
To find
pH of saturated lime water.
Formula
Solubility-limited concentration of OH-.
Solution
Saturated Ca(OH)2 (limewater) has pH ≈ 12 — quite basic but limited by low solubility.
Answer
(C)
Q39JEE Main 2018The formula of milk of magnesia is
AMg(OH)2
BMgO
CMg(NO3)2
DMgCl2
Easy idea
Milk of magnesia is a milky suspension of Mg(OH)₂ in water. Acts as antacid and laxative.
Given
Milk of magnesia is a suspension.
To find
Formula of milk of magnesia.
Formula
Standard nomenclature.
Solution
Milk of magnesia = Mg(OH)2 (suspended in water, used as antacid and mild laxative).
Answer
(A)
Q40JEE Main 2020Atomic radius of which alkali metal is smallest?
ALi
BNa
CK
DRb
Easy idea
Atomic radius grows down the group. Li sits at the top of Group 1, so it's the smallest.
Given
Atomic radius increases down the group.
To find
Smallest alkali metal.
Formula
Periodic trend.
Solution
Li has the smallest atomic radius (and ionic radius) in group 1.
Answer
(A)
Q41JEE Main 2017The chemical formula of gypsum is
ACaSO4·2H2O
BCaSO4·½H2O
CCaSO4
DCaCO3·MgCO3
Easy idea
Gypsum is the fully hydrated form: CaSO₄·2H₂O. Heat it to ~120 °C and water leaves to give POP.
Given
Hydrated calcium sulphate.
To find
Formula of gypsum.
Formula
Mineral fact.
Solution
Gypsum = CaSO4·2H2O (dihydrate). Heating gives Plaster of Paris.
Answer
(A)
Q42JEE Main 2019Sodium metal can be prepared by
ADown's process
BCastner process
CSolvay process
DBoth (a) and (b)
Easy idea
Down's process electrolyses molten NaCl. Castner electrolyses molten NaOH. Both make Na metal.
Given
Industrial preparations of Na.
To find
Process for preparing Na metal.
Formula
Down's: electrolysis of molten NaCl; Castner: electrolysis of molten NaOH (older method).
Solution
Both Down's process and Castner process are used (Down's is the modern method).
Answer
(D)
Q43JEE Main 2021Plaster of Paris reacts with water to form
AGypsum
BQuick lime
CSlaked lime
DLimestone
Easy idea
POP picks up water and hardens back into gypsum — that's why plaster sets when mixed with water.
Given
Reverse hydration of CaSO4·½H2O.
To find
Product when POP sets.
Formula
POP + 1.5 H2O → CaSO4·2H2O (gypsum) — the setting reaction.
Solution
POP sets back to gypsum (CaSO4·2H2O) on adding water. This is why POP hardens.
Answer
(A)
Q44JEE Main 2018Be differs from rest of Group 2 elements because
AIt does not form Be2+ ion in aqueous solution
BIts compounds are covalent
CIts hydroxide is amphoteric
DAll of the above
Easy idea
Be is the odd one out of Group 2 — covalent compounds, amphoteric hydroxide, and no free Be²⁺ ion in water. All three are true.
Given
Anomalous properties of Be.
To find
What makes Be different from Mg, Ca, Sr, Ba.
Formula
Small size and high polarising power.
Solution
All three — Be2+ doesn't exist as a free ion; Be compounds are largely covalent; Be(OH)2 is amphoteric.
Answer
(D)
Q45JEE Main 2022The hardness of water is expressed in terms of equivalents of
ACaSO4
BCa(OH)2
CCaCO3
DCaCl2
Easy idea
Water hardness is reported as if it were all CaCO₃ — in mg per litre (ppm) of CaCO₃ equivalent.
Given
Water hardness is reported in ppm of CaCO3 equivalent.
To find
Standard expression of hardness.
Formula
Hardness ppm = mg of CaCO3 equivalent per litre.
Solution
Hardness is expressed as ppm of CaCO3 equivalent.
Answer
(C)
Q46JEE Main 2019Among alkaline earth metals, the lightest metal is
ABe
BMg
CCa
DSr
Easy idea
Be is at the top of Group 2 with the smallest atomic mass, so it's the lightest alkaline earth metal.
Given
Density trends in alkaline earth metals.
To find
Lightest alkaline earth metal.
Formula
Be has the smallest atomic mass and small atomic volume gives a low density.
Solution
Be is the lightest alkaline earth metal (density 1.85 g/cm3).
Answer
(A)
Q47JEE Main 2020Which compound is used in the production of cement?
ACaO
BCaCO3
CCa(OH)2
DCaSO4
Easy idea
Cement is made by heating limestone (CaCO₃) with clay — limestone is the main raw material.
Given
Cement clinker is made from limestone.
To find
Raw material for cement.
Formula
Heating limestone with clay produces clinker.
Solution
Limestone (CaCO3) is the main raw material in cement production.
Answer
(B)
Q48JEE Main 2017When sodium is dissolved in liquid ammonia, the colour of the solution is
AYellow
BBlue
CRed
DBlack
Easy idea
Sodium dissolves in liquid ammonia to give 'free' electrons that absorb red light, so the solution looks blue.
Given
Alkali metals dissolve in liquid NH3 to give blue solutions of solvated electrons.
To find
Colour of Na in liquid ammonia.
Formula
Electrons absorb in red region ⇒ solution is blue.
Solution
Solutions are blue at low concentrations (solvated electrons); become bronze and conductive at higher concentrations.
Answer
(B)
Q49JEE Main 2021Which is more covalent?
ANaCl
BMgCl2
CBeCl2
DCaCl2
Easy idea
Fajans' rules: a small, highly-charged cation polarises the anion strongly. Be²⁺ wins on both counts, so BeCl₂ is the most covalent.
Given
Covalent character of chlorides depends on polarising power of cation (Fajans' rules).
To find
Most covalent chloride.
Formula
Smallest, most highly charged cation ⇒ most covalent.
Solution
BeCl2 — Be2+ has the highest charge density ⇒ greatest polarising power ⇒ most covalent.
Answer
(C)
Q50JEE Main 2022The order of solubility of group 2 sulphates in water is
ABeSO4 > MgSO4 > CaSO4 > BaSO4
BBaSO4 > CaSO4 > MgSO4 > BeSO4
CMgSO4 > BeSO4 > CaSO4 > BaSO4
DBeSO4 > BaSO4 > MgSO4 > CaSO4
Easy idea
Group 2 sulphates get less soluble down the group because Be²⁺'s huge hydration energy beats the rest.
Given
Solubility of group 2 sulphates decreases down the group.
To find
Order of sulphate solubility.
Formula
Lattice enthalpy nearly constant; hydration enthalpy decreases sharply down the group.
Solution
BeSO4 > MgSO4 > CaSO4 > SrSO4 > BaSO4. Be2+ has highest hydration enthalpy ⇒ most soluble.
Answer
(A)