Correct Answer - `a`
Thereofre, the order of acididc character:
Aromatic gt Non-aromaic gt Anti-aromatic.
But anti-aromati of `(III)` is more than `(II)` since `(III)` is more resonace stablised thatn `(II)`
Therefore, the order of decreasing acidic character of `K_(a)` value is `(I) gt (IV) gt (III) gt (II)`.
