AI-generated practice question — model-generated for extra practice, not a previous-year CBSE board question.
(A) Both A and R are true and R is the correct explanation of A.
Only about 10% of energy passes to the next trophic level; the rest is lost as heat. So very little usable energy remains beyond the fourth level, limiting food chain length to 3–4 steps.
The textbook explicitly states: "Since so little energy is available for the next level of consumers, food chains generally consist of only three or four steps. The loss of energy at each step is so great that very little usable energy remains after four trophic levels." This directly confirms both A and R, and R correctly explains why A is true. The 10% law is the key concept here.