Which of the following is a part of detritus food chain?

The correct answer is Option (1) → Earthworm

The detritus food chain starts with dead organic matter (detritus) and is run by decomposers and detritivores. In the figure the arrows from every level lead down to the decomposers.

Option (1) Earthworm — Correct. The detritus food chain begins with dead organic matter. Earthworms are detritivores: they feed on detritus and break it into smaller particles (fragmentation), so they are part of this chain.

Option (2) Birds — Incorrect. Birds such as the sparrow feed on living organisms; they are part of the grazing food chain.

Option (3) Man — Incorrect. Man feeds on living plants and animals, at the top of grazing food chains.

Option (4) Snake — Incorrect. A snake is a carnivore of the grazing food chain.

NCERT Extract:
Decomposition – “You may have heard of the earthworm being referred to as the farmer’s ‘friend’. This is so because they help in the breakdown of complex organic matter as well as in loosening of the soil. Similarly, decomposers break down complex organic matter into inorganic substances like carbon dioxide, water and nutrients and the process is called decomposition.”