Which of the following processes is responsible for the formation of a Delta when river water meets the sea water?
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → Coagulation
River water is a colloidal solution of clay, and sea water contains many electrolytes. When the two meet, the ions of the sea water neutralise the charge on the clay particles. The particles then come together and settle (coagulation), and the deposited clay builds up as a delta.
Why the other options are incorrect
Option (1) Peptization — Incorrect. Peptization is the reverse process — a precipitate is turned into a colloidal sol by adding a small amount of electrolyte.
Option (2) Colloid formation — Incorrect. The clay is already a colloid in river water; a delta forms when this colloid is destroyed, not formed.
Option (4) Emulsification — Incorrect. An emulsion is a liquid dispersed in another liquid (such as oil in water); clay in river water is a solid in a liquid.
Note: This question is from the pre-rationalised NCERT book (2022-23). The topic is not there in the latest NCERT book (2026-27), and it is also out of the CUET 2026 syllabus.
NCERT (Pre-rationalised edition, 2022-23):
Formation of Delta – “River water is a colloidal solution of clay. Sea water contains a number of electrolytes. When river water meets the sea water, the electrolytes present in sea water coagulate the colloidal solution of clay resulting in its deposition with the formation of delta.”