Cockroach is an insect because it has -
(a)Wings
(b)Six legs
(c)Compound eyes
(d)Trachea

Hint: Cockroach is an insect, hence it belongs to the Arthropoda phylum. The common features of all insects are a chitinous exoskeleton, a three-part body, three pairs of jointed legs, compound eyes, and one pair of antennae. Some of the features in the options are seen in other animals as well, but one of them is exclusively seen in insects.

Complete answer:
Cockroaches are common insects found in almost all environments including households. They are most common in tropic and subtropic environments.
- They are known as insects because they have six legs which are in the form of three pairs of jointed legs. The other features that distinguish insects from other animals are a chitinous exoskeleton, a three-part body of head, thorax, and abdomen, three pairs of jointed legs, compound eyes, and one pair of antennae.
- The pairs of legs, which are a form of jointed appendages, help in a swift movement.
- The wings are used in flight and are protected by the tegmina or the first set of wings.

Additional Information:
Wings are most commonly observed in birds, or the Aves.
- Compound eyes are also observed in crustaceans.
- Trachea is present in the organ systems of many animals such as birds, humans, centipedes, onychophorans, and others.
- Cockroaches breathe through tracheae, a system of tubes, which are attached to openings called spiracles on all body segments.
So, the correct answer is option (b) ‘six legs’.

Note: Common cockroach species in India include the American cockroach Periplaneta americana and the oriental cockroach Blatta orientalis.
Cockroaches belong to the order Blattodea which also includes termites.