Concept:A food chain must show a correct feeding order, where energy flows from producer to consumers progressively.
Explanation:In option B, grass is a producer, but a toad does not feed on grass.
Toads are insect-eaters, not plant-eaters.
Also, the grasshopper cannot consume a toad, because the chain has reversed the natural order.
Therefore, Grass → Toad → Grasshopper → Rat is not a possible food chain.
The other options follow a logical sequence of producers, primary consumers, and secondary consumers.
Answer:Option B — Grass → Toad → Grasshopper → Rat — is impossible.