Question

Which of the following is not an aerosol?
A) mud
B) dust
C) smoke
D) fog

Answer 1

aerosol is a suspension of soft and fine solid particles or liquid droplets in gas
Soo mud is more likely the and 4ur question

Answer 2

An aerosol is a suspension of fine solid particles or liquid droplets, in air or another gas with particle diameters in the range of 10−9 to 10−4 m.

Some of the examples of  aerosols are fog, dust, smoke, geyser steam etc.

They can be  natural or anthropogenic.

Mud is not an aerosol.