The correct option is C Infinity
Given,
Distance of the object from the mirror, u=20 m and radius of curvature, R=40 m
Let image distance =v.
We know, focal length, f=radius of curvature2 = 402
⇒f=20 m.
Using sign conventions we have u=−20 m and f=−20 m ( for concave mirror)
Using mirror formula
1v + 1u = 1f
1v + 1−20 = −120
1v = 0
v=−10 = ∞
So the image will form at infinity.