Calculate the percentage composition of oxygen in calcium nitrate.

$\text{ The formula of calcium nitrate is }\mathrm{Ca}{\left({\mathrm{NO}}_3\right)}_2\text{. Thus, the formula mass or molecular mass. }$

$=\text{ At mass of }\mathrm{Ca}+2\times \text{ At. Mass of }\mathrm{N}+6\times \text{ At. Mass of oxygen }$

$\begin{array}{l}=40+2\times 14+6\times 16=164\\ \mathrm{\%}\text{ of }\mathrm{Ca}=\frac{40}{164}\times 100=24\\ \mathrm{\%}\text{ of }\mathrm{N}=\frac{28}{164}\times 100=17\\ \mathrm{\%}\text{ of }\mathrm{O}=100-(24+17)=59\end{array}$