Define the angle of contact and state its any two characteristics.

Explanation

The angle of contact for a liquid-solid pair (a liquid in contact with solid) is defined as the angle between the surface of the solid and the tangent drawn to the free surface of the solid and the tangent drawn to the free surface of the solid and the tangent drawn to the free surface at the point of contact meausred inside the liquid.
Characteristics:
`(a)` The value of angle of contact depends on the nature of the liquid and solid in contact, and is constant for a given liquid-solid pair, other factors remaining unchanged.
`(b)` It depends upon the medium (gas) above the free surface of the liquid.
`(c )` The angle of contact changes due to impurity or temperature.