$Na_2S_2O_3$ reacts with moist $Cl_2$ to from $Na_2SO_4,HCl$ and $\underline{X}.$ Which one of the following is $\underline{X}$?

Question

$$(a)\;H_2S \quad (b)\;SO_2 \quad (c)\;SO_3 \quad (d)\;S$$