Sulphur disproportionates in hot alkali: $S + OH X^{-} S X^{2 -} + SO X_{3} X^{2 -} + H X_{2} O$ . For the balanced equation with smallest whole numbers, the total number of electrons transferred is

Answer: A

The balanced equation is

3 S + 6 OH X^{-} 2 S X^{2 -} + SO X_{3} X^{2 -} + 3 H X_{2} O

. One S goes 0 to +4 (loses 4 electrons) and 2 S go 0 to -2 (gain 2 each, total 4). So 4 electrons are transferred in the equation as written.