How many moles of magnesium phosphate, ${\mathrm{Mg}}_3({\mathrm{PO}}_4{)}_2$ will contain $0.25 \mathrm{mole}$ of oxygen atoms?

$2$ moles of ethyl alcohol are present in $6$ moles of water. What is the mole fraction of alcohol?

If the concentration of ${\mathrm{CO}}_2$ is $0.1 \mathrm{M}$ in a soda water bottle containing $200 \mathrm{mL}$ liquid, what is the volume of the dissolved ${\mathrm{CO}}_2$ at STP?

(Assume ${\mathrm{CO}}_2$ behaves like an ideal gas)

The equation $2\mathrm{Al}\left(\mathrm{s}\right)+\frac{3}{2}{\mathrm{O}}_2\left(\mathrm{g}\right)⟶{\mathrm{Al}}_2{\mathrm{O}}_3\left(\mathrm{s}\right)$ shows that: