The balanced chemical equation for methane combustion is:
\[
\mathrm{CH_4 + 2O_2 \rightarrow CO_2 + 2H_2O}
\]
This indicates that 1 mole of methane requires 2 moles of oxygen for complete combustion.
At S.T.P., 1 mole of any gas occupies 22.4 L. Thus, 2 moles of oxygen occupy:
\[
2 \times 22.4 = 44.8\ \text{L}
\]
Consequently, for 0.25 moles of methane, the volume of oxygen required is:
\[
0.25 \times 44.8 = 11.2\ \text{L}
\]