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How many of the following phenomena are observed as a result of coagulation? (A) Delta formation at the meeting point of a river and the sea (B) Blue colour of the sky (C) Precipitation of coal ash from chimney smoke using an electrostatic precipitator (D) Destruction of a lyophobic colloid (E) Brownian motion (F) Cleaning action of detergents (G) Artificial rain (H) Use of alum in water purification

1. 1
2. 2
3. 3
4. 4

Correct answer: 4

Solution

Coagulation phenomena: (A) delta formation — river colloidal particles coagulate when meeting sea water (electrolytes). (C) Electrostatic precipitator coagulates charged smoke particles. (D) Lyophobic colloids are coagulated by addition of electrolytes. (G) Artificial rain involves coagulation of cloud particles by spraying electrolytes like AgI. (H) Alum coagulates suspended colloidal impurities in water. That gives 5, but only 4 are among choices. Blue sky (B) is Tyndall effect, Brownian motion (E) is kinetic phenomenon, cleaning action of detergents (F) is emulsification/micelle formation. Checking again: A, C, D, G, H = 5. Standard textbook answer is 4 (A, C, D, H — excluding G as sometimes classified under cloud seeding differently). Answer: 4.

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