Solution:A dioptre, is a unit of measurement of the optical power of a lens, which is equal to the reciprocal of the focal length measured in meters (that is, 1/f metres). It is thus a unit of reciprocal length.Hence, P = 1/f ⇒ 2 = 1/f ⇒ 0.5 meter.
as the value is positive, it is a positive lens, that is, convex.
Hence, the option (c) is true.