Concept: This question tests the understanding of color vision in the human eye, specifically how different cone cells contribute to the perception of various colors.

Why (D) is correct: The human retina contains three types of cone cells, each sensitive to different wavelengths of light: red, green, and blue. When all three types of cones (red, green, and blue) are stimulated equally, their combined signals are interpreted by the brain as white light. This is the principle of additive color mixing, where combining primary colors of light in equal proportions results in white.

Why other options are wrong:

• (A) Red light: Would be perceived if only red cones were predominantly stimulated.
• (B) Green light: Would be perceived if only green cones were predominantly stimulated.
• (C) Blue light: Would be perceived if only blue cones were predominantly stimulated.

Common Mistake: Students might confuse additive color mixing (light) with subtractive color mixing (pigments), where mixing primary pigments (cyan, magenta, yellow) results in black.

NEET Tip: Remember that cones are responsible for color vision and function best in bright light, while rods are responsible for dim light (scotopic) vision and do not perceive color.

Correct Answer: (D)