question- primary function of crystalline lens in human eye is to

1) reduce intensity of light

2) adjust eye of pupil 

3) ffocus incidet light rays 

4) filter out dust particles

Dear Student!

The primary function of crystallline lens is to adjust focus of eye on objects at different distances.This adjustment of focus is similar to the focussing of a photographers camera ,and is contolled by the nervous system which activate the muscles around the lens to alter its shape and hence refractive power.

So the answer is 2) adjustment of pupil.