Use the following phase diagram for solid$-$liquid mixtures of sodium and potassium at equilibrium to answer the following questions.

a$)$ For each of the zones $($A through F$),$ indicate the species and their state of matter for each phase that exists at equilibrium.

b$)$ A solid$-$liquid separator operates with a feed stream of $85wt\%$ sodium and $15wt\%$ potassium. Determine the temperature that would produce the maximum amount of pure sodium and identify what percentage of the feed would be pure sodium at this temperature.