Answer
0.75 L $O_{2}$
Work Step by Step
The balanced chemical equation is
$2H_{2}+O_{2}\rightarrow 2H_{2}O$
At the same T and P, volumes of gases are proportional to the coefficients in the balanced chemical equation. Therefore,
$V(O_{2})=1.5\,L\,H_{2}\times\frac{1\,L\,O_{2}}{2\,L\,H_{2}}=0.75\,L$