Question 10

Given below are two statements : 

Statement I : When a capillary tube is dipped into a liquid, the liquid neither rises nor falls in the capillary. The contact angle may be $$0°$$. 

Statement II : The contact angle between a solid and a liquid is a property of the material of the solid and liquid as well. 

In the light of the above statement, choose the correct answer from the options given below.

We need to evaluate both statements about capillarity and contact angle.

Statement I: When a capillary tube is dipped into a liquid, the liquid neither rises nor falls. The contact angle may be $$0°$$.

If the liquid neither rises nor falls, the contact angle must be $$90°$$ (not $$0°$$). When the contact angle is $$0°$$, the liquid completely wets the surface and rises in the capillary. Statement I is false.

Statement II: The contact angle between a solid and a liquid is a property of the material of the solid and liquid as well.

This is correct. The contact angle depends on the nature of both the solid surface and the liquid (as well as the surrounding medium). It depends on the relative strengths of adhesive forces (solid-liquid) and cohesive forces (liquid-liquid). Statement II is true.

The correct answer is Option (3): Statement I is false but Statement II is true.

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