Explanation

Focal length and power are related by f (in metres) = 1/P, so f = 1/(-1.25) = -0.80 m, i.e. -80 cm. The negative sign indicates a diverging (concave) lens, which is the correction prescribed for myopia (short-sightedness) to diverge rays before they enter the eye. A convex lens would have positive power and is used for hypermetropia. The lens is therefore 80 cm in focal length and concave, option (D).