Question

The correct order of increasing thermal stability of the given compounds is
I. HF
II. HBr
III. HCl
IV. HI

• A. $I \, < \, II \, < \, III \, < \, IV$
• B. $IV \, < \, II \, < \, III \, < \, I$
• C. $IV \, < \, II \, < \, I \, < \, III$
• D. $II \, < \, IV \, < \, I \, < \, III$

Answer 1

Answer: (B)

Stability depends on bond strength Bond strength depends on bond length. Bond length depends on the size of halides. Bigger bond length easily cleavage of H $-X$ bond and thus, the correct order is $\text{HF}>\text{HCl}>\text{HBr}>\text{HI}$
$\text{IV} < \text{II} < \text{III} < \text{I}$