Which of the following insects undergo complete metamorphosis?

The insect that undergoes complete metamorphosis is the beetle. Complete metamorphosis, also known as holometabolism, is a developmental process consisting of four distinct life stages: egg, larva, pupa, and adult. Beetles, which belong to the order Coleoptera, exhibit this type of transformation, where the larval stage looks entirely different from the adult stage. This can be beneficial for survival, as each life stage can occupy different ecological niches and reduce competition for resources.

In contrast, ants, roaches, and grasshoppers undergo incomplete metamorphosis, also known as hemimetabolism. This process involves three stages: egg, nymph, and adult. In these cases, the nymphs generally resemble small adults and go through a series of molts to mature rather than undergoing a distinct transformation like beetles do. Therefore, beetles are the clear example of insects that undergo complete metamorphosis.