Give scientific reasons : We cannot clearly see an object kept at a distance less than 25 cm from the eye.

Answer: The eye lens cannot become thick enough to bring an object closer than 25 cm to a focus on the retina.

The eye lens changes its focal length with the help of the ciliary muscles, but this power of accommodation is limited. For an object nearer than the least distance of distinct vision (25 cm for a normal eye), the required focal length is smaller than the lens can provide, so the image forms behind the retina and looks blurred. The strain of trying also tires the eye.