CBSE Class 10 Science 2022 · Paper 31/2/1 · Question 7(a)

About $20,000$ J ($2\times 10^4$ J, that is $20$ kJ) would have been present in the grass. Justification: by the ten per cent law, only about $10\%$ of the energy at one trophic level is transferred to the next. The chain has five trophic levels - grass (1), grasshopper (2), frog (3), snake (4), peacock (5) - so going back from the peacock to the grass the energy is multiplied by $10$ four times: $2\to 20\to 200\to 2000\to 20,000$ J.