Question

Order of $K_a$ will be:

• A. I > II > III
• B. II > I > III
• C. I > III > II
• D. III > I > II

Answer 1

The correct option is C I > III > II

Stronger will be the acid when the conjugate base is stabilised more.

$\text{acidic strength}\propto -I,-M$
Here $N{O}_2$ will greater stabilise the conjugate base by -I and -M effect. While $-OMe$ group destailise the conjugate base by +M effect.
Since more the acidc strength, more will be the value of $K_a$. Hence the order becomes I > III > II.