Which one of the following four glass lenses is a diverging lens?

The correct answer is Option 2 (ii).

In optics, the nature of a lens (converging or diverging) is determined by its shape and the relative thickness of its center compared to its edges. A diverging lens (concave lens) is characterized by being thinner at the center than at the periphery. This geometry causes parallel rays of light to refract away from the optical axis.

• Option 2 (ii): This lens is a double concave lens. Since the central portion is thinner than the edges, it causes light rays to spread out or diverge, making it the only diverging lens among the choices.
• Options 1 (i) and 3 (iii): These represent convex lenses (biconvex and plano-convex). They are thicker at the center, which causes light rays to converge.
• Option 4 (iv): This is a positive meniscus lens, which also acts as a converging lens because the center remains thicker than the edges.