The SI unit of power of lens is:

Dioptre

The correct answer is option 2. Dioptre.

The power of a lens is a measure of its ability to bend light rays. It is quantified in dioptres (D), which is defined as the reciprocal of the focal length of the lens measured in meters.

For a converging lens (convex lens), which is thicker at the center than at the edges, the power is positive. This means that it converges light rays and can form real images.

For a diverging lens (concave lens), which is thinner at the center than at the edges, the power is negative. This indicates that it diverges light rays and forms virtual images.

Thus, the power of a lens, measured in dioptres, is the SI unit for quantifying its ability to refract light.