Answer
$3.0 \space moles \space H_2$ are needed to react with 1.0 mole of $N_2$.
Work Step by Step
1. Determine the conversion factor between $N_2$ and $H_2$ moles:
According to the coefficients: 3 moles $H_2$ = 1 mole $N_2$ .
$\frac{ 3 \space moles \space H_2}{ 1 \space mole \space N_2}$ and $\frac{ 1 \space mole \space N_2}{ 3 \space moles \space H_2}$
2. Use this conversion factor to calculate the amount of $H_2$ moles:
$1.0 \space moles \space N_2$ $\times$$\frac{ 3 \space moles \space H_2}{ 1 \space mole \space N_2} = 3.0 \space moles \space H_2$
