Which of the following describes a concave lens?

A concave lens is characterized by its inward-curving shape, resembling a cave, which is the reason for its name. This type of lens is designed to diverge light rays that pass through it. When parallel rays of light enter a concave lens, they spread apart or diverge, creating the effect of an image that appears to be located further away than it actually is. This divergence is a key feature of concave lenses, making them useful in various applications, such as correcting nearsightedness.

In contrast, other options describe different types of lenses or do not accurately represent a concave lens. A lens that bulges outward and converges light refers to a convex lens, which focuses light rays to a point. A flat lens does not have the curvature needed to bend light appreciably, and hence it does not produce the optical effects associated with concave lenses. Lastly, the mention of a lens used only in microscopes relates to a specific application rather than a defining characteristic of concave lenses in general. Concave lenses can be found in a variety of optical devices beyond microscopes.