Question

How many moles of hydrogen will be needed to react with 2 moles of nitrogen in the reaction `N_2 + H_2 -> NH_3`?

Answer 1

The balanced equation for dinitrogen reduction is:
`N_2(g) + 3H_2(g) rarr 2NH_3(g)`.

`2` `"moles"` `N_2` requires `6` moles `H_2`.

Explanation:

The equation above represents probably the most important inorganic reaction on the planet in that it allows the formation of ammonia and nitrates for nitrogenous fertilizer.

Your question specified 2 moles of nitrogen. I would be quite justified in assuming that the questioner meant 2 moles of dinitrogen gas, i.e. the equivalent of `4` moles of `"NITROGEN"` atoms.

Thus, if `2` moles of dinitrogen gas are specified, `6` moles of dihydrogen gas are required.