Given below are two statements : One is labelled as Assertion (A) and the other is labelled as Reason (R). Assertion (A): Clothes containing oil or grease stains cannot be cleaned by water wash. Reason (R): Because the angle of contact between the oil/grease and water is obtuse. In the light of the above statements, choose the correct answer from the option given below.

Both (A) and (R) are true and (R) is the correct explanation of (A)

Both (A) and (R) are true but (R) is not the correct explanation of (A)

Properties of Matter PYQ — JEE Main 2022 · 29 Jul · Shift 1 · Q54 with Solution

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Correct answer: A

Understand the assertion

Assertion (A): Clothes containing oil or grease stains cannot be cleaned by water wash.

This is true in the usual sense because oil/grease does not mix with water and does not get effectively removed by plain water.
Understand the reason

Reason (R): The angle of contact between oil/grease and water is obtuse.

This is also true in the relevant physical sense. When a liquid does not wet a surface, the contact angle is greater than $90^\circ$ (obtuse). Water does not wet oily/greasy surfaces properly, so it cannot spread over and remove the stain effectively.
Link between wetting and cleaning

Cleaning by water requires that water should wet the stained surface/fibres of the cloth.
- If the contact angle is acute $(<90^\circ)$ , wetting is good.
- If the contact angle is obtuse $(>90^\circ)$ , wetting is poor.
Since oil/grease makes the surface non-wettable by water, water fails to penetrate and detach the stain.
Conclusion
- Assertion (A) is true.
- Reason (R) is true.
- Reason (R) correctly explains Assertion (A).

Therefore, the correct option is:

$\boxed{\text{A}}$