The initial volume of a gas cylinder is 750.0 mL. If the pressure of gas inside the cylinder changes from 840.0 mmHg to 360.0 mmHg, the final volume of the gas will be

Using Boyle's law, we have

$V_f=\frac{V_{\mathrm{i}}{p}_{\mathrm{i}}}{p_{\mathrm{f}}}=\frac{\left(750.0\mathrm{mL}\right)\left(840\mathrm{mmHg}\right)}{\left(360\mathrm{mmHg}\right)}=1750\mathrm{mL}=1.750\mathrm{L}$

The volume of the gas inside the cylinder will not change even if the pressure inside the cylinder decreases as a result of partial gas escape or a drop in temperature.