The value of contact angle for kerosene with solid surface?
(A) ${0^ \circ }$
(B) ${90^ \circ }$
(C) ${45^ \circ }$
(D) ${33^ \circ }$

Hint: Here we should first understand the concept of contact angle. The contact angle is the angle which is measured conventionally through the liquid, where a liquid-vapour interface meets a solid surface. It is used to quantify the wettability of a solid surface by a liquid using the Young equation.

Complete answer:
The contact angle generally depends on the medium above the free surface of the liquid and also on the nature of the liquid and solid that are in contact. It is not dependent on the inclination of the solid that is in contact. It changes with change in the surface tension and also with the temperature and the purity of liquid. If any liquid wets the solid completely, then the contact angle will be zero. If the molecules of the liquid are strongly attracted to the molecules of the solid then the liquid drop will completely spread out on the solid surface, corresponding to a contact angle of ${0^ \circ }$. Thus, the value of contact angle for kerosene with a solid surface is ${0^ \circ }$.

Therefore, the correct answer is option A.

Note: The contact angle is generally used to quantify the wettability of a solid surface by a liquid using the Young equation. Contact angles are generally very sensitive to contamination. The values reproducible to better than a few degrees are usually obtained only under laboratory conditions with liquids that are purified and very clean solid surfaces.