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.
