The volume of chlorine that can completely react with 100mg of hydrogen at STP is 

${\mathrm{H}}_2 +{\mathrm{Cl}}_2 \stackrel{ }{\to } 2\mathrm{HC}l$

1 mol of H₂ = 1 mol of Cl₂. 

$$\begin{gathered} {\mathrm{n}}_{{\mathrm{H}}_2}= \frac{100 \mathrm{X}\hspace{0.17em}{10}^3}{2}= 5\times {10}^{-2}\mathrm{mol} \\ \mathrm{moles} \mathrm{of} \mathrm{chlorine} \mathrm{reacted} = 5\times {10}^{-2}\mathrm{mol} \\ \mathrm{Volume} \mathrm{of} \mathrm{chlorine} \mathrm{reacted} = 22.4 \mathrm{X}\hspace{0.17em}5\times {10}^{-2}\mathrm{mol}= 1120\mathrm{ml} \end{gathered}$$