According to Gay-Lussac's law, 3 volumes of H2 will give 2 vol. of NH3 . ∴67.2L‌of‌H2 will give =
2×67.2
3
=44.8L‌of‌NH3 At the same time, 3 vol. of H2 will react =1 vol. of N2. ∴67.2L of H2 will react =
1
3
×67.2L of N2=22.4L of N2 67.2L of H2 and 22.4L of N2 are required to form 34g of NH3. So, for 3.4g of NH3 6.72L and 2.24L of H2 and N2 gas are required respectively.