Given below are two statements: One is labelled as Assertion (A) and the other…
2020
Given below are two statements: One is labelled as Assertion (A) and the other is labelled as Reason (R):
Assertion (A): Solar ponds store solar energy in the form of heat.
Reason (R): Solar ponds contain water with definite gradient of salt concentration.
In the light of the above statements, choose the most appropriate answer from the options given below:
- A.
Both (A) and (R) are correct and (R) is the correct explanation of (A)
- B.
Both (A) and (R) are correct but (R) is NOT the correct explanation of (A)
- C.
(A) is correct but (R) is not correct
- D.
(A) is not correct but (R) is correct
Show answer & explanation
Correct answer: A
Concept
A solar pond is a body of saline water designed to collect and retain solar thermal energy. Salt is dissolved so that its concentration rises with depth, creating a density gradient (a halocline) that is saltiest — and hence densest — at the bottom. This non-convecting saline layer suppresses natural convection: although heating alone would make the bottom layer buoyant, its very high salt content keeps it denser than the cooler, less-salty water above it, so it cannot rise past the gradient, and the absorbed heat stays trapped at the bottom instead of mixing upward and escaping.
Application
Evaluate the assertion and the reason against this principle:
Assertion: A solar pond does store incoming solar radiation as heat in its lower zone, so the assertion is a true statement.
Reason: The pond is indeed built with a definite increasing gradient of salt concentration with depth, so the reason is a true statement.
Link: That salt-concentration gradient is exactly what blocks convection and lets the heat accumulate and remain stored. The reason therefore states the very mechanism that makes the assertion happen.
Cross-check
Remove the salinity gradient and the pond behaves like ordinary water: heated bottom water rises, mixes, and the heat is quickly lost to the surface and atmosphere. Because the storage of heat depends on the salt gradient, the reason is not merely a coincidental true fact alongside the assertion but the actual explanation of it. Hence both statements are true and the reason correctly explains the assertion.