Answer
$5.00$ moles of $O_2$ are necessary to react with 2.00 moles of $C_2H_2$.
Work Step by Step
1. Find the mole-mole conversion factors:
According to the coefficients: 2 moles $C_2H_2$ = 5 moles $O_2$
$\frac{ 2 \space moles \space C_2H_2}{ 5 \space moles \space O_2}$ and $\frac{ 5 \space moles \space O_2}{ 2 \space moles \space C_2H_2}$
2. Use the mole-mole conversion factors to calculate the amount of equivalent $O_2$ in moles:
$ 2.00$ moles $C_2H_2 \times \frac{ 5 \space moles \space O_2}{ 2 \space moles \space C_2H_2} = 5.00$ moles $O_2$
