Phosphorus and sulfur form a series of binary compounds. The best characterized are P₄S₃, P₄S₇, and P₄S₁₀, all of which melt congruently. Assuming that only these three binary compounds of the two elements exist,

(a) draw schematically only the P/S phase diagram. Label each region of the diagram with the substance that exists in that region and indicate its phase. Label the horizontal axis as x_S and give the numerical values of x_S that correspond to the compounds. The melting point of pure phosphorus is 44°C and that of pure sulfur is 119°C.

(b) Draw, schematically, the cooling curve for a mixture of composition x_S = 0.28. Assume that a eutectic occurs at x_S = 0.2 and negligible solid–solid solubility.