[PPSC Principal, HM and BPEO, 2020]

23. Butter floats in droplets on the surface of a hot soup. But when the soup cools, the droplets spread out to form a thin layer on the surface. This happens because

1. Butter is less dense than the soup

2. Butter is more viscous than the soup

3. Surface tension of the soup increases on cooling

4. Butter forms an insulation layer to slow down cooling

Correct Answer :

Surface tension of the soup increases on cooling