The minimum distance of clear vision for a normal healthy eye of human being is supposed to be

The answer is D (25 cm). This is the near point of a normal young adult eye: the closest distance at which an object can be seen clearly without strain. Clear vision is possible at any distance from this near point out to infinity, which is the far point.

The core concept is accommodation. The ciliary muscles change the curvature and thickness of the crystalline lens to focus on near objects. Once the lens is at its maximum curvature, the image can no longer be focused sharply, and that limit is the near point.

• A) 50 cm is too far. It is closer to the near point of an older person whose accommodation has weakened, not a healthy young eye.
• B) 10 cm is too close. A normal eye cannot focus that near without strain.
• C) 15 cm is also too close for a normal eye to focus comfortably.

The 25 cm figure is also the standard reference distance used in magnifying power and microscope calculations. For UPSC, link it to eye defects: in hypermetropia the near point moves farther away, and in presbyopia it recedes with age.

Trap: Aspirants sometimes confuse the near point with the far point, or pick the value that looks like a typical reading distance. Remember that 25 cm is the standard value for a normal eye.