Question

A mercury drop does not spread on a glass plate because the angle of contact between glass and mercury is
A. Acute
B. Obtuse
C. Zero
D.\[{90^ \circ }\]

Answer 1

Hint:Cohesion and adhesion are the properties of the molecules of a substance. In these forces, the molecules of the substance are attracted either to or to the molecules of a different substance.

Complete step by step solution:
A mercury drop does not spread on the glass plate. This is because glass is solid and the molecules of a solid are attracted strongly and stuck to each other so that they should not get attracted to the other surface they come in contact with. So, it can be said that the force of attraction is greater among the molecules of glass than with the molecules of mercury.

That means the force of cohesion when the glass comes in contact with mercury is greater than the force of adhesion between the glass and the mercury. As a result, a mercury drop does not spread on a glass plate because the angle of contact between the glass and mercury is obtuse.

Hence, option B is the correct answer.

Note:It is important to note that the force of cohesion is nothing but an intermolecular force of attraction between the molecules of two same types. For example, water molecules can form droplets because they have a strong intermolecular force of attraction among each other. But the force of adhesion is between the molecules of two different types of substances so they can be attracted to each other. For example: applying fevicol to any substance, makes the fevicol stick with that substance due to the force of adhesion between them.