Question

A ray of light makes an angle of 10° with the horizontal above it and strikes a plane mirror which is inclined at an angle O to the horizontal. The angle O for which the reflected ray becomes vertical is (a) 40°. (B)50°. (C)80°. (D) 100°

Answer 1

180 - (40 * 2) = 100°

So the answer is (D) 100°

Hope this helps! :)