Q1: A volatile substance added to a paint to make its application easy and smooth, is known as

ANS:B - solvent

A solvent is a material which dissolves another material. For example, when you add water to salt or sugar, they dissolve in water forming a solution. In other words, a solution contains a solvent in which the solute or the material is completely dissolved.

The thinner is only added to the paint (mixture) with the role of reducing the viscosity, but not to dissolve any ingredients.