Mechanical Properties of Fluids — Physics STD 12 Science — Question

When a liquid is in contact with a solid, the angle between the tangent drawn to the free surface of the liquid and the surface of the solid at the point of contact measured inside the liquid is called the angle of contact.
Characteristics of the angle of contact:
a. The angle of contact is constant for a given liquid-solid pair.
b. The value of the angle of contact depends upon nature of liquid and solid in contact.
c. It depends upon the medium which exists above the free liquid surface.
d. The angle of contact changes due to impurity or temperature.