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

The reaction is $H_2+{Cl}_2\to 2 HCl$

According to reaction same volume of both the reactants induldge to form 2 moles of hydrogen chloride.

$100 mg$ hydrogen $=0.05$ moles $=1120 mL$

Since the amount of both reactant are same chlorine required for $100 mg$ hydrogen is $1120 mL$.

Hence option A is the correct answer.