PHASE EQUILIBRIUM $($a$)$ A pure substance A has a liquid vapor pressure of $320$ mm Hg at $125\backslash$deg C$,800$ mm Hg at $150\backslash$deg C$,$ and $60$ mm Hg at the triple point. The melting point of A decreases slightty as pressure $85\backslash$deg C$.$ increases. $($i$)$ Sketch a phase diagram for A$.($ii$)$ From the phase diagram, estimate the boiling point. $($iii$)$Explain in detail what changes occur when, at a constant pressure of $320$ mm Hg$,$ the temperature drops from $150\backslash$deg to$100\backslash$deg C$?[15$ marks$]$