(C) Assertion (A) is true, but Reason (R) is false.
Assertion is correct — a food web is indeed a network of several interconnected food chains. However, Reason is false — a food web increases (not decreases) the stability of an ecosystem by providing alternative pathways for energy flow.
The textbook states that each organism is generally eaten by two or more other organisms, forming a food web (Fig. 13.3). A food web increases ecosystem stability because if one food chain is disrupted, energy can still flow through alternate chains. The Reason reverses this fact, making it false — so option (C) is correct.