Final answer:
To double the equilibrium concentration of ammonia, add 0.100 mol of hydrogen.
Step-by-step explanation:
To double the equilibrium concentration of ammonia, we need to add more hydrogen to the mixture.
According to the balanced equation for the reaction, 3 moles of hydrogen are required to produce 2 moles of ammonia.
Therefore, if we want to double the concentration of ammonia, we need to add an additional 0.100 mol of hydrogen (0.100 mol NH3 / 2 = 0.050 mol H2).