Question

Values of dissociation constant \( K_a \) are given as follows: 
 

Correct order of increasing base strength of the conjugate bases \( {CN}^-, {F}^- \) and \( {NO}_2^- \) is: 
 

• A. \( {F}^-<{CN}^-<{NO}_2^- \)
• B. \( {NO}_2^-<{CN}^-<{F}^- \)
• C. \( {F}^-<{NO}_2^-<{CN}^- \)
• D. \( {NO}_2^-<{F}^-<{CN}^- \)

Hint:

A lower \( K_a \) of an acid corresponds to a stronger conjugate base.

Answer 1

The Correct Option is C

Step 1: Understanding the relation between \( K_a \) and base strength.
- The strength of a conjugate base is inversely related to the acid's \( K_a \) value.
- A lower \( K_a \) value means a weaker acid and a stronger conjugate base.
Step 2: Arranging the bases.
- \( {HCN} \) has the lowest \( K_a \), meaning \( {CN}^- \) is the strongest base.
- \( {HNO}_2 \) has a moderate \( K_a \), so \( {NO}_2^- \) is a weaker base than \( {CN}^- \).
- \( {HF} \) has the highest \( K_a \), meaning \( {F}^- \) is the weakest base.