$6.90\,\text{g}$ of an ammonium salt is heated with excess aqueous sodium hydroxide. The volume of ammonia given off, measured under room conditions, is $2.51\,\text{dm}^3$. Which ammonium salt has been used?
- Aammonium carbonate ($M_r = 96.0$)
- Bammonium chloride ($M_r = 53.5$)
- Cammonium nitrate ($M_r = 80.0$)
- Dammonium sulfate ($M_r = 132.1$)