Option C: elements produce spectra with only few distinct lines.
The spectra are not continuos and are different for every element. This permits to identify elements.
Answer: 6 moles
Take a look at the balanced chemical equation for this synthesis reaction
N 2(g] + 3 H 2(g] → 2 NH 3(g]
Notice that you have a 1:3 mole ratio between nitrogen gas and hydrogen gas. This means that, regardless of how many moles of nitrogen gas you have, the reaction will always consume twice as many moles of hydrogen gas.
So, if you have 2 moles of nitrogen taking part in the reaction, you will need
2 moles N 2 ⋅ 3 moles H 2 /1 mole N 2 = 6 moles H 2
