The least distance of distinct vision for a normal human eye is approximately:

Correct — B. The least distance of distinct vision is the minimum distance at which the eye sees an object most distinctly without strain. It is also called the near point.

NCERT's Class 10 chapter on the human eye puts it at about 25 cm for a young adult with normal vision. The far point is infinity, so a normal eye sees clearly from 25 cm outwards: option (b).

Why the others are wrong

• (a)
  2.5 cm — 2.5 cm is a tenth of the near point. A page held that close blurs, because the eye lens cannot shorten its focal length below a certain minimum.
• (c)
  2.5 m — 2.5 m lies inside the range a normal eye already sees clearly, 25 cm to infinity. It is ten times the near point, not the near point itself.
• (d)
  25 m — 25 m sits well inside the clear range of a normal eye, which runs from the near point, about 25 cm, out to infinity. It is no limit at all.

Accommodation is the eye lens changing its focal length. The ciliary muscles contract to thicken the lens for near objects and relax to thin it for distant ones.

The focal length cannot fall below a minimum, and that sets the near point, about 25 cm. The far point of a normal eye is at infinity.

Key facts

• Least distance of distinct vision = near point = about 25 cm for a young adult with normal vision (NCERT Class 10 Science).
• The far point of a normal eye is at infinity.
• In hypermetropia the near point is farther than 25 cm, and a convex lens corrects it.

Common traps

• Swapping the near point (about 25 cm) with the far point (infinity).
• Reading 25 cm but ticking 25 m: all four options use the digits 2 and 5 and differ only in the decimal point and the unit.

No directly related past PYQ was found.