Which measuring instrument consists of a metal triangular frame supported on three legs, used to measure the radius of curvature of an object such as lenses and curved mirrors which are spherical in shape?

Correct option is B

A spherometer is a measuring device that has a metallic triangular frame supported on three legs. The tips of the three legs form an equilateral triangle and lie on the radius. There is a central leg which can be moved in a perpendicular direction. Below is the experiment on how to determine the radius of curvature of a given spherical surface by a spherometer.