Reason : If centre of mass of an isolated system is already at rest, it remains at rest.
A. Assertion is correct, reason is correct; reason is not a correct explanation for assertion
B. Assertion is correct, reason is correct; reason is a correct explanation for assertion.
C. Assertion is incorrect, reason is correct
D. Assertion is correct, reason is incorrect
Answer:A
Reason : If centre of mass of an isolated system is already at rest, it remains at rest.
A. Assertion is correct, reason is correct; reason is not a correct explanation for assertion B. Assertion is correct, reason is correct; reason is a correct explanation for assertion. C. Assertion is incorrect, reason is correct D. Assertion is correct, reason is incorrect