The molar mass of a compound can be determined by the freezing point depression method. The solution must be relatively dilute and you must know the molal freezing point depression constant of the solvent, Kf. Which statement regarding Kf is true? A. Kf should be small so that the solvent will not sublimate.
B. Kf will change depending on what solute is dissolved in the solvent.
C. Kf should be negative so the freezing point of the solution will decrease.
D. Kf should be large so the temperature change will be large enough to measure.

K should be large so the temperature change will be large enough to measure.

Explanation:

Let us recall that;

∆T = k m I

Where;

∆T= change in boiling point

K= freezing point constant

m= molality

i= Van't Hoff factor

Since the change in temperature depends on k, the larger the value of k the larger the temperature change(Ts - Tb). Hence; K should be large so the temperature change will be large enough to measure.

Ts= freezing temperature of pure solvent

Tb= freezing temperature of solution

c. heat could easily travel through the molecules in the air and escape/enter the flask. removing the air slows down the heat transfer.  

b.final