The table lists the physical properties of three compounds. What could P, Q and R be?
- AP: MgO, Q: KCl, R: $\text{NH}_3$
- BP: MgO, Q: NaF, R: $\text{C}_2\text{H}_5\text{Br}$
- CP: $\text{SiO}_2$, Q: KCl, R: $\text{C}_2\text{H}_5\text{Br}$
- DP: $\text{SiO}_2$, Q: NaF, R: HCl