Give reasons for the following :

(a)

Food web is more stable than a food chain in an ecosystem.

(b)

A food chain should not have more than four to five trophic levels.

Greater number of alternatives in the form of variety of organisms available at each trophic level in an ecosystem.

The available energy keeps on decreasing at each trophic level according to $\displaystyle 10$ percent law. So more trophic levels lead to less energy at the last trophic level which is not enough for the organisms to survive.