Final answer:
One mole of elemental nitrogen reacts with two moles of elemental hydrogen to produce one mole of hydrazine, therefore the correct substance amount is 2 moles of hydrogen (H2).
Step-by-step explanation:
The correct amount of the substance that would react with nitrogen gas (N2) to form one mole of hydrazine (N2H4) is 2 moles of hydrogen (H2). This is based on the chemical equation for the synthesis of anhydrous hydrazine:
N2(g) + 2H2(g) → N2H4(l)
From the equation, it is clear that one mole of elemental nitrogen reacts with two moles of elemental hydrogen to produce one mole of hydrazine. Therefore, the correct answer is (b) 2 H2.