Select the option that is appropriate regarding the following two statements labelled Assertion and Reason. Assertion: In lined canals, the increased velocity eliminates the possibility of silting in the canal bed. Reason: Canal lining provides a smooth and stable surface and thus, the velocity of the flow can be increased.
- ABoth Assertion and Reason are false.
- BBoth Assertion and Reason are true and Reason is the correct explanation of Assertion.Correct
- CAssertion is true, but Reason is false.
- DBoth Assertion and Reason are true, but Reason is not the correct explanation of Assertion.
Solution
Concept
Lining makes the canal surface smooth (low roughness), so velocity increases and silt does not settle.
Formula
V = (1/n) R2/3 S1/2
Step-by-step solution
1. Lining gives a smooth, stable surface with a low Manning's n. 2. Lower n gives higher velocity for the same slope (V = (1/n) R2/3 S1/2). 3. A lined surface also does not erode, so a high velocity is safe. 4. Higher velocity keeps silt in suspension, so silting of the bed is avoided. 5. Both statements are true, and the Reason explains the Assertion. Answer is B.
Explanation
A lined canal has a smooth and hard surface, so water can flow at a higher velocity without scouring. This higher velocity keeps sediment moving and prevents silting. So the Reason correctly explains the Assertion.
Why the other options are wrong
A: Both statements are true, not false. C: The Reason is true, because lining allows higher velocity. D: The Reason directly explains why silting is removed, so D is wrong.
Shortcut
Lining → smooth → higher V → no silting: a direct cause-effect chain, so pick B.
Common mistake
Choosing D because the word 'eliminates' seems too strong. The standard textbook answer treats it as true.
Correct answer: B) Both Assertion and Reason are true and Reason is the correct explanation of Assertion.