Which topology is the least commonly used?

The least commonly used topology among the options provided is the ring topology. In a ring topology, each device is connected to exactly two other devices, forming a circular pathway for data transmission. This setup can lead to issues such as data collisions or single points of failure, as the entire network can be disrupted if one connection fails.

While ring topology has advantages in certain applications, like predictable latency due to data traveling in one direction, it is less favored in modern networking due to these vulnerabilities and a lack of scalability compared to other topologies. For instance, star topology is widely used because it is easy to install and manage, allowing devices to connect centrally to a hub or switch. Similarly, bus topology, though less common than star, is simple and cost-effective for small networks. Mesh topology, while complex and more expensive, offers high redundancy and reliability, making it favorable for critical applications.

In summary, the ring topology is less commonly adopted in contemporary networks due to its susceptibility to failures and limitations in scalability, making it the correct choice among the given options.