The correct answer is (a) Concave mirror only.
Explanation:
A real image is formed when light rays converge to a point after reflecting off a mirror. Concave mirrors can converge light rays under certain conditions, allowing them to form a real image.
Why other options are incorrect:
(b) Plane mirror only: Plane mirrors only reflect light rays, causing them to appear to come from behind the mirror, resulting in a virtual image.
(c) Convex mirror only: Convex mirrors always diverge light rays, meaning they cannot form a real image. They only produce virtual images.
(d) Both concave and convex mirrors: Since convex mirrors only create virtual images, this option is incorrect.