Explanation

(d)
$K_{1}$ for, $N_{2} + 3H_{2} \rightleftharpoons 2{NH}_{3}$
$K_{2}$ for, $NH_{3} \rightleftharpoons \frac{1}{2}N_{2} + \frac{3}{2}H_{2}$
$\therefore K_{1} \times K_{2} = \frac{\left\lbrack NH_{3} \right\rbrack^{2}}{\left\lbrack N_{2} \right\rbrack\left\lbrack H_{2} \right\rbrack^{3}} \times \frac{\left\lbrack N_{2} \right\rbrack^{1/2}\left\lbrack H_{2} \right\rbrack^{3/2}}{\lbrack NH_{3}\rbrack}$
or, $K_{1} \times K_{2} = \frac{1}{K_{2}}$
$\therefore K_{2} = \frac{1}{\sqrt{K_{1}}}$