Question

Compare the acidic strength of the following acids:

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

Answer 1

The correct option is B $I>III>IV>II$

$\text{Stability of conjugate base}\propto \text{Strength of acidity}$
$-C{H}_3$ group at ortho and para positions, show $+H$ effect, which increase the electron density and destabilise the conjugate base.
Hence, compound (IV) and (II) are less acidic.
Comparing (I) and (III), $C{H}_3$ at meta position shows +I effect which will increase electron density and destabilise the conjugate base. Thus, (III) is less acidic than (I).

Comparing (II) and (III), compound (II) is least acidic because $C{H}_3$ is located at ortho position, so that it shows more +I effect than $C{H}_3$ at para position.
Therefore, the order of acidic strength is