Final answer:
When a concave lens with a lower refractive index is immersed in a medium with a higher refractive index, it remains shaped as a concave lens but does not effectively diverge light; it does not become a b/ converging lens.
Step-by-step explanation:
When a concave lens of refractive index 1.5 is immersed in a medium of refractive index 1.65, the nature of this lens changes. In air or any medium with a refractive index lower than that of the lens, a concave lens is a diverging lens because it causes parallel light rays to spread out, or diverge, after passing through it. However, when the surrounding medium's refractive index is higher than that of the lens, the lens no longer causes the light rays to diverge.
In this specific case, the lens is still shaped like a concave lens, but the effect it has on light rays is determined by the relative refractive indices of the lens and the surrounding medium. Since the refractive index of the medium (1.65) is higher than the refractive index of the lens (1.5), the lens can't diverge light as it would in air and it loses its diverging effect, but it does not become a converging lens. The nature of the lens does not become converging; rather, it becomes less effective at diverging light.