Which one of the following is NOT an example of commensalism?

The correct answer is Option (4) → Cuckoo and the crow

Option (1) An orchid growing on a mango branch — Commensalism. NCERT gives an orchid growing as an epiphyte on a mango branch as an example: the orchid benefits while the mango tree gets no apparent benefit.

Option (2) Barnacles growing on the back of whale — Commensalism. Barnacles growing on the back of a whale benefit, while the whale derives no apparent benefit. One partner gains and the other is unaffected.

Option (3) Cattle egret and grazing cattle — Commensalism. The egret gains insects stirred up by the cattle.

Option (4) Cuckoo and the crow — Not commensalism. The cuckoo laying eggs in the crow’s nest is brood parasitism.

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. The egrets always forage close to where the cattle are grazing because the cattle, as they move, stir up and flush out insects from the vegetation that otherwise might be difficult for the egrets to find and catch. Another example of commensalism is the interaction between sea anemone that has stinging tentacles and the clown fish that lives among them. The fish gets protection from predators which stay away from the stinging tentacles. The anemone does not appear to derive any benefit by hosting the clown fish.”
Population Interactions – “… Try to follow the movements of the cuckoo (koel) and the crow in your neighborhood park during the breeding season (spring to summer) and watch brood parasitism in action.”