How many liters of hydrogen gas are needed to react completely with 50.0 L of chlorine gas at STP?

50L of H2

Explanation:

First let us generate a balanced equation for the reaction

Cl2 + H2 - > 2HCl

From the equation above,

1L of Cl2 required 1L of H2 for complete reaction.

Therefore, 50L of Cl2 will also require 50L of H2 for complete reaction.