Which of the following is an example of commensalism?

The correct answer is Option (4) → All of the above

In commensalism, one species benefits and the other is neither harmed nor benefited (+/0). All three options are the book’s own examples of this interaction.

Option (1) Orchid growing as an epiphyte on a mango branch — Correct statement, but it is only one of the correct points, so on its own it is not the answer. The orchid gets a place high up in the light. The mango tree is neither harmed nor helped.

Option (2) Barnacles growing on the back of a whale — Correct statement, but it is only one of the correct points, so on its own it is not the answer. The barnacles get a surface to live on and are carried to new places. The whale gets no apparent benefit and is not harmed.

Option (3) Cattle egret foraging near grazing cattle — Correct statement, but it is only one of the correct points, so on its own it is not the answer. As the cattle move, they stir up insects from the grass, and the egrets catch them. The cattle neither gain nor lose.

NCERT Extract:
Population Interactions – “(iv) Commensalism: This is the interaction in which one species benefits and the other is neither harmed nor benefited. An orchid growing as an epiphyte on a mango branch, and barnacles growing on the back of a whale benefit while neither the mango tree nor the whale derives any apparent benefit. The cattle egret and grazing cattle in close association, a sight you are most likely to catch if you live in farmed rural areas, is a classic example of commensalism.”