Number of moles of Hydrogen $\left({\mathrm{H}}_2\right)=\frac{m}{M}=\frac{16}{2}=8$

Number of moles of oxygen $\left({\mathrm{O}}_2\right)=\frac{128}{32}=4$

Using ideal gas equation, $PV=nRT$,

Where pressure $P=1 \mathrm{atm}=1.01\times {10}^5 \mathrm{Pa} \left(\mathrm{STP}\right)$

Putting the values, 

$1.01\times {10}^5 \mathrm{V}=\left(8+4\right)\times 8.314\times 273$

$V=\frac{12\times 8.314\times 273}{1.01\times {10}^5}{ \mathrm{m}}^3$

$=0.27\times {10}^6{ \mathrm{cm}}^3=27\times {10}^4{ \mathrm{cm}}^3$