What type of lens is formed by a bubble inside water?

Explanation

(i) Biconvex lens is the lens formed when an air bubble is inside water. (ii) The air bubble acts as a diverging lens (concave lens) in water. (iii) This makes it equivalent to two convex interfaces meeting each other with light entering from a medium with a higher refractive index. (iv) Therefore an air bubble in water acts as a concave lens made of glass does in air.