A lens having a power of $-2\,\text{D}$ means —

• aIt is a convex lens of focal length 2 m
• bIt is a concave lens which diverges a parallel beam such that the rays appear to diverge from a point 2 m from the optical centre
• cIt is a plane glass with no focal length
• dIt is a convex lens of focal length 0.5 m