Question

Identify the correct statements
I. Lithium halides are somewhat covalent in nature
II. NaNO$_3$ on heating gives NO$_2$ gas
III. LiHCO$_3$ is a solid
IV. All alkali metals form ethynides on reaction with ethyne

• A. I, II, III only
• B. II, IV only
• C. I only
• D. I, III only

Hint:

Apply Fajans' rule for covalent character in ionic compounds. Check thermal decomposition products of nitrates. Verify stability of alkali bicarbonates and ethynide formation trends.

Answer 1

The Correct Option is C

1. Statement I: Lithium halides (e.g., LiCl) have covalent character due to Li$^+$'s high charge density (Fajans' rule), making I correct.
2. Statement II: NaNO$_3$ decomposes on heating to NaNO$_2$ + O$_2$, not NO$_2$, so II is incorrect.
3. Statement III: LiHCO$_3$ is not stable as a solid; it exists in aqueous solution, unlike other alkali bicarbonates, so III is incorrect.
4. Statement IV: Only Li, Na, K form ethynides (e.g., Li$_2$C$_2$) with ethyne; Rb, Cs do not, so IV is incorrect.
5. Thus, only I is correct, so the answer is (3) I only.