Calculate the volume of O₂ at STP required to completely burn 100 ml of acetylene.

The balanced equation is
$\begin{array}{l}\underset{\left(\mathrm{g}\right)}{{\mathrm{C}}_2{\mathrm{H}}_2}+\underset{\left(\mathrm{g}\right)}{\frac{5}{2}{\mathrm{O}}_2}\to \underset{\left(\mathrm{g}\right)}{2{\mathrm{CO}}_2}+{\mathrm{H}}_2\mathrm{O}\\ {\mathrm{C}}_2{\mathrm{H}}_2 = \frac{5}{2}{\mathrm{O}}_2; 1\mathrm{mole} = \frac{5}{2}\mathrm{mole}\\ 22400\mathrm{ml}\text{ at }\mathrm{STP}=\frac{5}{2}\text{ x22400ml mole at STP }\\ 100\mathrm{ml}=?\\ =\frac{5}{ 2}\times \frac{22400\times 100}{2}\times 22400 = 250 \mathrm{ml}\end{array}$