Question

when does a Ray of light falling on a lens pass through it undeviated​

Answer 1

When it pass with pole or optical centre

Answer 2

Optical centre

$\bullet$ When the ray passes through the optical centre (denoted by O) of the lens, it passes undeviated.

Note:

$\bullet$ This only happens for one special ray.

$\bullet$ The ray that is parallel to the optical axis and goes through the center of the lens.

$\bullet$ All other rays are deviated to some extent.