The solubility of potassium nitrate at $20°\mathrm{C}$is $32 \mathrm{g}$ per $100 \mathrm{g}$ of water. How much salt is required to prepare$66 \mathrm{g}$ of its saturated solution?

Two chemical species $\mathrm{X}$ and $\mathrm{Y}\mathrm{}$combine together to form a product $\mathrm{P}$ which contains both $\mathrm{X}$ and $\mathrm{Y}$, $\mathrm{X}\mathrm{}+\mathrm{}\mathrm{Y}\to \mathrm{P},\mathrm{}\mathrm{X}$ and $\mathrm{Y}$ cannot be broken down into simpler substances by simple chemical reactions. Which of the following concerning the species $\mathrm{X},\mathrm{}\mathrm{Y}$ and $\mathrm{P}$ are correct?

(i) P is a compound

(ii) X and Y are compounds

(iii) X and Y are elements

(iv) P has a fixed composition