When a certain amount of octane, ${\mathrm{C}}_8{\mathrm{H}}_{18}$ is burnt completely, 7.04 gm ${\mathrm{CO}}_2$is formed. What is the eight of ${\mathrm{H}}_2\mathrm{O}$formed, simultaneously?

We have 

$$\begin{gathered} W_{{\mathrm{H}}_2\mathrm{O}}=\frac{7.04}{44}\times \frac{1}{8}\times 9\times 18 \\ =3.24 \mathrm{g} \end{gathered}$$

When a certain amount of octane, ${\mathrm{C}}_8{\mathrm{H}}_{18}$ is burnt completely, 7.04 gm ${\mathrm{CO}}_2$is formed. 3.24 g is the eight of ${\mathrm{H}}_2\mathrm{O}$formed, simultaneously