Question
Question: The correct order of pK<sub>a</sub> of following substance in aqueous solution is 
A
(i) > (ii) > (iii) > (iv)
B
(iv) > (iii) > (ii) > (i)
C
(ii) > (iii) > (iv) > (i)
D
(i) > (iii) > (ii) > (iv)
Answer
(ii) > (iii) > (iv) > (i)
Explanation
Solution
* Presence of two EWG and resonance stablisation makes (i) strongest acid
* In (ii), two NH2 group acts as ERG through resonance after the loss of H+ therefore loss of H+ is most difficult