Answer
0.5 mole of $A_2B$ will be produced.
Work Step by Step
This is a reaction with limiting and excess reactant.
1.0 mole of A can only produce 0.5 mole of $A_2B$, because each product molecule requires 2 of A.
1.0 mole of B would be able to produce 1.0 mole of $A_2B$, but it would be necessary to have 2.0 moles of A.
