Final answer:
The light rays come out parallel when light originates from the left of a diverging lens at its focal point, where in this case, the focal length is 25cm.
Step-by-step explanation:
When light originates from a point 25cm to the left of a diverging lens, and it comes out the other side with completely parallel rays, it indicates that the point of origin coincides with the lens's focal point. The correct answer to why the rays come out parallel is because c) The focal length is 25cm. A diverging lens, which is concave in shape, causes rays of light entering it parallel to its axis to diverge. The light rays appear to originate from the focal point. If an object is placed at the focal point of a diverging lens, the outgoing rays will be parallel. Here, since the focal length is negative, having light originate 25cm (the focal length) from the lens means that it is originating from the focal point.