Mean free path depends on:

$\mathrm{Mean} \mathrm{free} \mathrm{path}=\frac{\mathrm{kT}}{\sqrt{2}{\mathrm{\pi d}}_{{\mathrm{m}}^2}{\displaystyle \frac{\mathrm{N}}{\mathrm{V}}}}$

k=Boltzmann constant

T=Temperature

d=diameter

$\frac{\mathrm{N}}{\mathrm{V}}=\mathrm{number} \mathrm{of} \mathrm{molecules} \mathrm{per} \mathrm{unit} \mathrm{of} \mathrm{volume}$

(A) With the increase in size of the molecule, the diameter of the molecule increases, therefore the space between the molecules decreases. This results in increased collisions and thereby decreases the mean free path.
(B) When density increases, the molecules are closer to each other. Thereby, increasing the number of collisions and resulting in decreasing mean free path
(C) With the increase in diameter of the molecule, the space between the molecules decreases. This results in increased collisions and thereby decreases the mean free path.