We use the Ideal Gas Equation to access the molar quantity of dioxygen gas............
$n=(PV)/(RT)=(0.927*atmxx0.4981*L)/(0.0821*(L*atm)/(K*mol)xx418.4*K)=1.34xx10^-2*mol$.
Given the stoichiometric equation..........
$Mg(s) + O_2(g) rarr MgO(s)$
There are $1.34xx10^-2*molxx24.31*g*mol^-1=??*g$ metal required for stoichiometric equivalence.