Assertion. A repeater is not like an amplifier.

Reason. A repeater regenerates a signal thereby removing noise.

(a)

Both Assertion and Reason are true and Reason is the correct explanation of Assertion.

Explanation
A repeater is not like an amplifier because a repeater not only amplifies the signal but also performs signal regeneration. When a signal weakens over long distances, the repeater collects the inbound packet and then retransmits it as if it were originating from the source station. This process effectively removes noise.