How many of the following are correct order with respect to the property mentioned? (i) Order of stability: CsO 2 RbO 2 KO 2 NaO 2 (ii) Order of melting points : LiF

Question

How many of the following are correct order with respect to the property mentioned?

(i) Order of stability: $CsO_{2} > RbO_{2} > KO_{2} > NaO_{2}$

(ii) Order of melting points : $LiF < LiCl < LiBr > Lil$

(iii) Thermal stability of peroxides : $Na_{2} O_{2} < K_{2} O_{2} < Rb_{2} O_{2} < Cs_{2} O_{2}$

(iv) Order of standard enthalpy of formation (only magnitude) $LiF > NaF > KF > RbF > CsF$

(v) Order of solubility : LiOH < NaOH < KOH < RbOH < CsOH

(vi) Order of solubility : $BeSO_{4} > MgSO_{4} > CaSO_{4} > BaSO_{4}$

(vii) Order of Thermal stability: $Li_{2} CO_{3} > Na_{2} CO_{3} > K_{2} CO_{3} > Rb_{2} CO_{3} > Cs_{2} CO_{3}$

TestHub · Accepted Answer

(i) Correct. Stability of superoxides increases down the group due to better lattice energy stabilization by larger cations.

(ii) Incorrect. The order should be LiF > LiCl > LiBr > LiI. Melting points decrease with increasing anion size due to decreasing lattice energy.

(iii) Correct. Thermal stability of peroxides increases down the group as the larger cation stabilizes the larger peroxide anion (O₂²⁻) better.

(iv) Correct. Enthalpy of formation (magnitude) decreases down the group due to decreasing lattice energy as cation size increases.

(v) Correct. Solubility of alkali metal hydroxides increases down the group due to decreasing lattice energy outweighing the decrease in hydration energy.

(vi) Correct. Solubility of alkaline earth metal sulfates decreases down the group due to decreasing hydration energy outweighing the decrease in lattice energy.

(vii) Incorrect. Thermal stability of carbonates increases down the group (Cs₂CO₃ > Rb₂CO₃ > K₂CO₃ > Na₂CO₃ > Li₂CO₃) due to increasing stabilization of the large carbonate anion by larger cations.

Therefore, 5 statements are correct.

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