Which of the following statements is incorrect?

The correct answer is Option (3) → Parasites that feed on the external surface of the host organism are called endoparasites.

Parasites are of two kinds. Ectoparasites feed on the external surface of the host, like lice on humans and ticks on dogs. Endoparasites live inside the host body, in the liver, kidney, lungs or red blood cells. The question asks for the one statement that is wrong.

Option (1) In amensalism, one species is harmed whereas the other is unaffected. — A correct statement. In amensalism one species is harmed whereas the other is unaffected.

Option (2) Predation, parasitism and commensalism share a common characteristic – the interacting species live closely together. — A correct statement. In predation, parasitism and commensalism the interacting species live closely together.

Option (3) Parasites that feed on the external surface of the host organism are called endoparasites. — An incorrect statement. Parasites that feed on the external surface of the host are called ectoparasites, not endoparasites.

Option (4) The life cycles of endoparasites are more complex because of their extreme specialisation. — A correct statement. Endoparasites are extremely specialised, so their life cycles are more complex.

NCERT Extract:
Population Interactions – “… In amensalism on the other hand one species is harmed whereas the other is unaffected. Predation, parasitism and commensalism share a common characteristic– the interacting species live closely together.”
Population Interactions – “… Parasites that feed on the external surface of the host organism are called ectoparasites. The most familiar examples of this group are the lice on humans and ticks on dogs.”
Population Interactions – “… In contrast, endoparasites are those that live inside the host body at different sites (liver, kidney, lungs, red blood cells, etc.). The life cycles of endoparasites are more complex because of their extreme specialisation.”