Question

What type of lens is an air bubble insode water?

Answer 1

obviously concave lenses are used in the air bubble i.......

Answer 2

the answer is concave lens.

reason:
the refractive index of air (medium 1) is less than the refractive index of water(medium 2),it acts as a diverging lens(concave lens) thus, the ray of light bends away from the normal with respect to point of incident if its moving from water to air.
the rays bend towards the normal when moving from air to water.

hope it helps!!