The X-chromosome linked colour blindness affects the ability to detect the difference between which of the following lights ?

Color blindness is most commonly an X-linked recessive genetic disorder. The genes responsible for the photopigments in the cone cells that detect red and green light are located on the X chromosome. A mutation or deficiency in these genes results in the inability to distinguish between red and green hues.

• Red-green color blindness: Since it is X-linked, it affects males more frequently than females because males have only one X chromosome.
• Blue-yellow color blindness: This is much rarer and is typically an autosomal trait (linked to Chromosome 7), meaning it is not X-linked.

Because the question specifically mentions X-chromosome linked color blindness, it refers to the red-green type, making option A the correct answer.