The power of a lens is defined as the reciprocal of its focal length in meters. In this question, we are given that the focal length of the biconvex lens is 25 cm.

To calculate the power of the lens, we need to convert the focal length from centimeters to meters.

1 cm is equal to 0.01 meters. So, we can convert the focal length as follows:

25 cm = 25 × 0.01 meters = 0.25 meters

Now, we can calculate the power of the lens by taking the reciprocal of the focal length (in meters):

Power = 1 / 0.25 = 4 dioptre

Therefore, the correct answer is option-1, +4 dioptre.

Alert - correct answer should be option-3, +0.04 dioptre.