The correct answer is option 3 - retina.

The retina is a vital part of the human eye on which the image is formed. It is located at the back of the eye and consists of specialized light-sensitive cells called photoreceptors. These photoreceptors, known as rods and cones, convert the incoming light into electrical signals that are then transmitted to the brain through the optic nerve. They play a crucial role in our ability to see and perceive visual information.

Option 1 - pupil is not the correct answer. The pupil is the opening in the center of the iris through which light enters the eye. It controls the amount of light that enters the eye by contracting or dilating.

Option 2 - cornea is also not the correct answer. The cornea is the transparent outer layer of the eye that helps to focus light onto the retina. It acts as a protective barrier for the eye.

Option 4 - iris is not the correct answer either. The iris is the colored part of the eye that controls the size of the pupil and helps regulate the amount of light that enters the eye.

Therefore, the correct answer is option 3 - retina.