(d)
$\sin{x - \sqrt{3}\cos{x = 2\sin\left( x - \frac{\pi}{3} \right)}}$
Since, $\ \ \ - 2 \leq 2\sin{\left( x - \frac{\pi}{3} \right) \leq 2}$
$\Rightarrow \ \ \ \ - 1 \leq 1 + 2\sin{\left( x - \frac{\pi}{3} \right) \leq 3}$
$\therefore$ Range of $S = \lbrack - 1,\ 3\rbrack$