Determine the percentage of oxygen in ammonium nitrate.

Step 1. Ammonium nitrate (${\mathrm{NH}}_4{\mathrm{NO}}_3$)

Step 2. Mass percentage $=\frac{\mathrm{Atomic}\mathrm{weight}}{\mathrm{Total}\mathrm{molecular}\mathrm{weight}}\times 100$

Step 3. Molecular weight of ${\mathrm{NH}}_4{\mathrm{NO}}_3$

$=4\mathrm{g}+28+48$

$=80\mathrm{g}/\mathrm{mole}$

Mass percentage of oxygen (O) in ammonium nitrate

$=\frac{48}{80}\times 100$

$=60\%$

Therefore, percentage of oxygen in Ammonium nitrate is $\mathbf{60}\mathbf{\%}$