Answer is: mass of hydrogen is 2.28 grams.
Balanced chemical reaction: 3H₂ + N₂ → 2NH₃.
m(NH₃) = 12.95 g; mass of ammonia.
n(NH₃) = m(NH₃) ÷ M(NH₃).
n(NH₃) = 12.95 g ÷ 17.03 g/mol.
n(NH₃) = 0.76 mol; amount of ammonia.
From chemical reaction: n(H₂) : n(NH₃) = 3 : 2.
n(H₂) = 3 · 0.76 mol ÷ 2.
n(H₂) = 1.14 mol; amount of hydrogen.
m(H₂) = 1.14 mol · 2 g/mol.
m(H₂) = 2.28 g; mass of hydrogen.
