Answer
See the answer below.
Work Step by Step
Number of moles of silane, from ideal gas law:
$P.V=n.R.T$
$n=(356\ mmHg/760\ mmHg×1\ atm)×5.20\ L/0.082057\ L.atm/mol.K/(25+273)\ K$
$n=0.0996\ mol$
From stoichiometry: $0.199\ mol$ of $O_2$
From ideal gas law:
$P.V=n.R.T$
$V=0.082057\ L.atm/mol.K×0.199\ mol×(25+273)\ K/(425\ mmHg/760\ mmHg×1\ atm)$
$V=8.71\ L$
