An Important Reaction Sequence in the Industrial Production of Nitric $\to$

An important reaction sequence in the industrial production of nitric acid is the following: N₂(g) + 3H₂(g) $\to$ 2NH₃(g)
4NH₃(g) + 5O₂(g) $\to$ 4NO(g) + 6H₂O(l)
Starting from 20.0 mol of nitrogen gas in the first reaction, how many moles of oxygen gas are required in the second one?

A) 12.5 mol O₂
B) 20.0 mol O₂
C) 25.0 mol O₂
D) 50.0 mol O₂
E) 100. mol O₂