The correct answer is (c) Red.
A rainbow is an optical and meteorological phenomenon that causes a spectrum of light to appear in the sky when the Sun shines onto droplets of moisture in the Earth’s atmosphere. Rainbows can be full circles. However, the observer normally sees only an arc formed by illuminated droplets above the ground, and centered on a line from the Sun to the observer’s eye.
The rainbow colors are always in the same order, with red on the outside and violet on the inside. This is because the different colors of light have different wavelengths. Red light has the longest wavelength, and violet light has the shortest wavelength. When sunlight hits a water droplet, the light is refracted (bent) as it enters the droplet. The light is then reflected off the back of the droplet and refracted again as it exits the droplet. The different colors of light are refracted by different amounts, so they are separated into a spectrum of colors.
The color red is seen in the middle of a rainbow because it is the color of light with the longest wavelength. The other colors of light have shorter wavelengths, so they are seen on the outside of the rainbow.