Ammonia is produced by the following reaction.

The answer, as you appear to have guessed, is
A) 7.5 moles of hydrogen would be needed to consume the available hydrogen. 

The atomic mass of N2 is 2 x 14 = 28, so 70 grams is 2.5 moles. 
The ratio of N2 to H2 in the equation is 3 to 1, so 7.5 mol of hydrogen would be needed to consume the available nitrogen. 
7 grams of H2 is only about 3.5 moles.