(d)
$H_{2} + I_{2} \rightleftharpoons 2HI$
$\lbrack HI\rbrack = 0.80,\ \left\lbrack H_{2} \right\rbrack = 0.10,\ \left\lbrack I_{2} \right\rbrack = 0.10$
$K_{c} = \frac{\lbrack HI\rbrack^{2}}{\left\lbrack H_{2} \right\rbrack\left\lbrack I_{2} \right\rbrack} = \frac{0.80 \times 0.80}{0.10 \times 0.10} = 64$