Correct Answer - a
Our eys are the sence organs for vision. The light sensitive inner layer of eyeball called retina contain photoreceptors viz. rod and cone cells which convert the energy of specific wvelengths of light into action potentials of nerve fibres. Rods are sensitive even to dim light and consequencly enable to see in dim light and at right. They contain a purple coloured photosensitive pigment, called rhodopsin, Rhodopsin derivative of vitamin A which is required for proper vision and is required for the regeneration of rhodopsin after if has been exposed to light.