The objective of a reflecting telescope is a:

The correct answer is Option (2) → Concave mirror

A reflecting telescope forms the first image by reflection instead of refraction. Its objective is a large concave mirror (often parabolic), which collects light from the distant object and brings it to a focus; an eyepiece then magnifies this image.

A mirror objective has no chromatic aberration, a parabolic mirror removes spherical aberration, and a mirror can be supported over its whole back, so it can be made much larger than a lens.

Option (1) Convex lens — Incorrect. A convex lens is the objective of a refracting telescope.

Option (2) Concave mirror — Correct. The concave mirror gathers and focuses the light in a reflecting telescope.

Option (3) Concave lens — Incorrect. A concave lens diverges light and cannot form a real image of a distant object.

Option (4) Prism — Incorrect. A prism disperses or deviates light; it is not used as an objective.

NCERT (2026-27):
Telescope – “… For these reasons, modern telescopes use a concave mirror rather than a lens for the objective. Telescopes with mirror objectives are called reflecting telescopes. There is no chromatic aberration in a mirror.”