Question

Arrange the following labelled hydrogens in decreasing order of acidity:

• A. $b>c>d>a$
• B. $c>b>a>d$
• C. $b>a>c>d$
• D. $c>b>d>a$

Answer 1

The correct option is A $b>c>d>a$

Acidic strength is directly proportional to the stability of conjugate base formed.

The conjugate base formed by removal of $H_b$ is stabilised by equivalent resonating structures. Hence, it is most stable and most acidic.

The conjugate base formed by removal of $H_c$ is stabilised by resonance effect of $N{O}_2$ whereas conjugate base formed by removal of $H_d$ is stabilised by -I effect of $N{O}_2$
Hence, $H_c$ is more acidic than $H_d$

Conjugated base formed by removal of $H_a$ is stabilised by electronegative $sp$ carbon but it is the least compared to others.

Hence, correct order of acidic strength
$b>c>d>a$