$ \Delta G^{\circ} = -2.303 \: RT\: log \: K_{eq}$
$= -2.303 \times (8.314 \: J/Kmol)(298\: K)(log\: K_{eq})$
$= -2.303 \times 8.314 \times 298 \times log(1.8 \times 10^{-7} ) = 38.484\: kJ/mol$
$ \Delta G^{\circ} - T \Delta S^{\circ} = \Delta H^{\circ}$
$ \Rightarrow \Delta S^{\circ} = \large\frac{\Delta H^{\circ}- \Delta G^{\circ} }{ T}$$ = \large\frac{(28.4 – 38.498)}{298}$$ = -33.8\: J/Kmol $
Ans : (A)