# $n$ moles of an ideal gas at temperature $T$ (in kelvin) occupy $V\; L$ of volume, exerting a pressure of $P$ atmospheres. What is the concentration (in $mol/L$) ?
( A ) $\frac{RT}{P}$
( B ) $\frac{R}{PT}$
( C ) $\frac{PT}{R}$
( D ) $\frac{P}{RT}$