Question

Which of the following will have lower $p{K}_a$ value ?

• A. $H_a$
• B. $H_b$
• C. $H_c$
• D. $H_d$

Answer 1

The correct option is A $H_a$

$H_a$ will have lower pKa value.

The order of Aromatic stability is : Aromatic > Non-aromatic > Anti- aromatic.

$\left(I\right)>\left(II\right)>\left(IV\right)>\left(III\right)$
(IV) has more resonating structures than (III) and is therefore more stable.
Therefore, $H_a$ in (I) is more acidic since it will give $H^{+}$ faster to become a stable aromatic anion.