A lens has a focal length of +25 cm. The power of this lens is:
Correct: A
The power of a lens (P) is the reciprocal of its focal length (f) in meters. P = 1/f(m). Given f = +25 cm, convert it to meters: f = +0.25 m. So, P = 1 / 0.25 = +4 Dioptres (D). The positive sign indicates it is a convex (converging) lens.