The minimum distance at which an eye with normal vision can see clearly and comfortably is about _____ cm.

• Our eyes can see at different distances by changing the focal length of the convex lens present in the eye. 
• The focal length of the eye lens is changed when ciliary muscles attached to the lens contract or relax.
• The focal length of the lens can't be reduced beyond a certain point therefore, we can't see very clearly if objects are kept very close to our eyes. 
• Objects must be held at a minimum of 25 cm from the eyes in order to see them comfortably and clearly. This is called the near point of the eye.

Therefore, 25 cm is the correct option.