$($a$).$ Briefly explain the following terms:

i$.$ Ideal and non$-$ideal solutions

ii$.$ Raoult's law

$($b$).$ Clearly compare the departure of electrolytes and non$-$electrolytes from ideal behavior.

$($c$).$ Benzene and toluene form nearly ideal solutions. Consider a solution of $1\mathrm{.}0$mol benzene and $3\mathrm{.}0$mol toluene. At $20C$ the vapour pressures of pure benzene and toluene are $9\mathrm{.}9$kPa and $2\mathrm{.}9$kPa, respectively. The solution is boiled by reducing the external pressure below the vapour pressure.

Calculate the:

i$.$ pressure when boiling begins,

ii$.$ composition of each component in the vapour,

iii. vapour pressure when only a few drops of liquid remain.

Assume that the rate of vaporization is low enough for the temperature to remain constant at $20C.$