Choose the correct option for the total pressure (in atm.) in a mixture of $4 \,g\, O _{2}$ and $2 \,g \,H _{2}$ confined in a total volume of one litre at $0^{\circ} C$ is :
$\left[\right.$ Given $\left.R = 0.082 \,L \,atm\, mol ^{-1} K ^{-1}, T =273\, K \right]$