question_answer

The correct order of\[p{{K}_{a}}\]value of the given carboxylic acids is

A)  (iii) < (i) < (iv) < (ii)

B)  (ii) < (iv) < (i) < (iii)

C)   (iv) < (ii) < (i) < (iii)

D)  (iii) < (i) < (ii) < (iv)

Correct Answer: C

Solution :

                 \[p{{K}_{a}}\]value is highest for weak acid. Presence of electron    withdrawing    groups    (like \[N{{O}_{2}},Cl\])on benzene nucleus stabilises the benzoate ion by dispersing charge and thus increase acidity. On the other hand, electron releasing groups like\[\text{ }NH{{ & }_{2}},\] destabilises the benzoate ion by intensifying charge and thus decrease acidity or\[{{K}_{a}}\](or increase\[p{{K}_{a}}\]value). Thus, the correct order of \[p{{K}_{a}}\]of given acids is