The least distance for distinct vision for a normal person is:
A. 1 m
B. 25 cm
C. 10 cm
D. None of these

Hint: Least distance for distinct vision is defined as the closest distance an object can be seen by someone with normal vision comfortably without any strain on their eye and the muscles responsible to adjust the eye lens.

Complete step-by-step answer:
In the human eye, the lens is adjusted by the muscles in the eye, this changes the distance from the retina and the focal length of the lens so that bright sharp image is formed at the retina. But even the amount of change that can be done by the muscles is limited and to view the objects closer to the eye, strain is required to be applied on the muscles, which can be harmful for the eye. It is possible to view objects closer than the least distance for distinct vision but doing that causes strain on our eye. For a normal adult human being that distance is 25 cm. It can be a bit different for different people but the average is around 25 cm. Hence, the correct option is B, i.e. 25 cm.

So, the correct answer is “Option B”.

Note: However, the least distance for distinct vision for an adult human being is 25 cm, it keeps on changing throughout the entire life of a human being. For babies it is 5-8 cm and keeps on increasing as humans age. This happens because the muscles in the eye that control the lens and move it and change its focal length become weaker due to their use over our lifetime and by the time we reach adulthood, the least distance for distinct vision becomes 25 cm.