What is the exoskeleton of an insect?

The exoskeleton of an insect is the hardened outer covering that provides structure and support, making option B the correct answer. This structure is primarily composed of chitin, a tough and flexible material that helps protect the insect's internal organs and prevents water loss, which is vital for survival, particularly in terrestrial environments. The exoskeleton also provides points of attachment for muscles, allowing for movement and locomotion.

Insects do not have an internal skeleton (like vertebrates), so their exoskeleton is crucial for their physical integrity and overall functionality. The other options refer to different aspects of insect anatomy or physiology that do not describe the exoskeleton. For instance, the internal organs, chemical composition, and reproductive systems are integral to the insect's biology, but they are not associated with the structural role fulfilled by the exoskeleton.