(s) about s-block elements and their…

(s) about s-block elements and their compounds.

One or more options correct

Choose the correct statement(s) about s-block elements and their compounds.

A. $\mathrm{LiCl}$ is soluble in ethanol and pyridine, whereas $\mathrm{NaCl}$ is nearly insoluble in them.
B. $\mathrm{Be(OH)_2}$ dissolves in both dilute acid and excess alkali.
C. The solubility of the sulfates of the alkaline earth metals in water decreases from $\mathrm{BeSO_4}$ to $\mathrm{BaSO_4}$ .
D. Potassium superoxide, $\mathrm{KO_2}$ , is diamagnetic.

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Answer: A, B, C

(A) True. The small

\mathrm{Li^+}

polarises

\mathrm{Cl^-}

, so

\mathrm{LiCl}

has appreciable covalent character (Fajans' rules) and dissolves in organic solvents like ethanol and pyridine;

\mathrm{NaCl}

is essentially ionic.
(B) True.

\mathrm{Be(OH)_2}

is amphoteric:

\mathrm{Be(OH)_2+2H^+\to Be^{2+}+2H_2O}

and

\mathrm{Be(OH)_2+2OH^-\to[Be(OH)_4]^{2-}}

.
(C) True. Down the group the lattice enthalpy of the large sulfate falls only slightly, while hydration enthalpy of the cation falls markedly, so the solubility decreases (

\mathrm{BeSO_4}

and

\mathrm{MgSO_4}

are soluble,

\mathrm{BaSO_4}

is insoluble).
(D) False. The superoxide ion

\mathrm{O_2^-}

has 17 valence electrons, with one unpaired electron in the

\pi^*

orbital, hence

\mathrm{KO_2}

is paramagnetic.
Correct options: (A), (B), (C).

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Original question written in the JEE Advanced 2022 Paper 2 pattern and checked twice for the correct answer. Not an official question paper. How we write and check questions · Corrections policy · Report a mistake