CBSE Class 10 Science 2020 · Paper 31/2/1 · Question 18(a)

(a) $\text{Grass}\to \text{Grasshopper}\to \text{Frog}\to \text{Snake}$ (producer, herbivore, carnivore, top carnivore); any correct four-level terrestrial chain is accepted. (b) Food energy can no longer pass to the higher levels: the organisms of the next higher level lose their food and decline, while the organisms of the level below are no longer eaten and increase in number. The food chain and the ecosystem become unbalanced. (c) By the 10% law, energy at level III $=10\%$ of $2000$ J $=200$ J, and energy at level IV $=10\%$ of $200$ J $=20$ J.