Answer
8.6 atm
Work Step by Step
$P_{total}V=n_{total}RT$
$\implies P_{total}=\frac{n_{total}RT}{V}$
$=\frac{[n(H_{2})+n(Cl_{2})]RT}{V}$
$=\frac{[\frac{3.0\,g}{2.016\,g/mol}+\frac{140.\,g}{70.9\,g/mol}](0.0821\,L\,atm\,mol^{-1}K^{-1})(301\,K)}{10.\,L}$
$=8.6\,atm$
