Chapter 3 - Stoichiometry - Active Learning Questions - Page 127: 16

0.5 moles of $A_2B$

The mole ratio of A to B in the chemical equation if $\frac{2}{1}$. However, the ratio of the number of moles of A to moles of B is $\frac{1}{1}$. Therefore, A is the limiting reactant. Because for every mole of A that we consume, 0.5 moles of $A_2B$ is produced, we produce 0.5 moles of $A_2B$.