Which of the following limits the number of trophic levels in a food chain?

Which group of organisms are not constituents of a food chain?

(i) Grass, lion, rabbit, wolf

(ii) Plankton, man, fish, grasshopper

(iii) Wolf, grass, snake, tiger 

(iv) Frog, snake, eagle, grass, grasshopper

In the given figure, the various trophic levels are shown in a pyramid. At which trophic level is maximum energy available?

What will happen if deer is missing in the food chain given below?

Grass $\to$ Deer $\to$ Tiger