The near point and far point of a person are 40 cm and 250 cm respectively. Determine the power of the lens he/she should use while reading a book kept at a distance 25 cm from the eye.

If the individual can construct the image of the book at a distance of 40 cm from his eyes, he will be able to read it. However, the book is 25 centimetres away. Therefore, a converging lens (convex) with the proper focal length is required. The graphic might help you understand it better.

To move an object's image 25 cm from the eye to the perigee of the flaw, the lens should be built. The lens, therefore, centimeters adheres to the following lens equation. 

$P= \frac{1}{f} and \frac{1}{f}= \frac{1}{v} - \frac{1}{u}$

$Hence, P = \frac{1}{ -0.4}-\frac{1}{-0.25}=1.5D$

$P = 1.5 D$

Hence, the correct answer is option C.