Question

food chain generally consists of three or four trophic levels why justify

Answer 1

it is because the energy get reduces as it travel from one tropic to another tŕopic level through the ten per cent law . So if the tropic level increase there is very little energy transferred to that animal

Answer 2

due to the loss of energy at every level is great, that only 10% of energy transfer to the next level and at last very little energy remains to use after the four trophic level
that's why in general food chain consists of three or four trophic levels.