An optical device X forms an image CD for an object AB as shown in the figure. The device X is a:

Correct option is A

The correct answer is (A) concave mirror.

Explanation:
A concave mirror can form both real and virtual images depending on the position of the object. If the object is placed beyond the focus, the concave mirror forms a real, inverted image. The image formed as CD from the object AB in this case suggests the characteristics of a concave mirror.

Incorrect Options Explanations:

•  Convex lens: Incorrect, as a convex lens typically forms a real or virtual image depending on the object distance.
• Convex mirror: Incorrect, convex mirrors always form virtual, upright images.
•  Concave lens: Incorrect, a concave lens forms only virtual, upright images.

Information Booster:

• Concave Mirror: A converging mirror that can form both real and virtual images based on the object's distance from the mirror.
• Real Image: Formed when the object is beyond the focal point and is inverted.
• Virtual Image: Formed when the object is within the focal point and is upright.