The general gas equation may be applied to calculate the $M_r$ of a gas. For a gas sample with a mass of $m$ grams, which expression gives the value of $M_r$?
- A$M_r = \frac{mRT}{pV}$
- B$M_r = \frac{pVRT}{m}$
- C$M_r = \frac{mpV}{RT}$
- D$M_r = \frac{pV}{mRT}$