Answer
No, it won’t be a converging lens when placed in water. It will actually become a diverging lens.
Work Step by Step
See the diagram.
The material’s index of refraction, n = 1.25, is higher than that of air (n =1.0003). A converging lens designed for use in air is thicker in the middle than it is at the rim.
However, the material’s index of refraction, n = 1.25, is lower than that of water (n=1.33).
Light rays speed up and bend away from the normal when entering the lens from water.
When light rays exit the lens back into water, they slow down and bend toward the normal.
As we can see from the diagram, in a situation when the lens is made of material whose index of refraction is lower than that of its surroundings, a lens that is thicker in the middle than it is at the rim will act as a diverging lens.
