Which of the following network topologies is the least secure and least…

Correct answer: Bus

A bus topology uses a single shared backbone cable. If the backbone fails, communication across the network can stop. It also has no alternate path between devices.

By contrast, mesh has multiple paths, star is easier to manage though the hub is a central point of failure, and tree gives hierarchical segmentation. So among the listed topologies, bus is the least secure and least reliable.