Answer : 3. "7"
Explanation :

1. Sunlight has seven colors.

2. Seven colours – violet, indigo, blue, green, orange, yellow and red.

3. Violet has the shortest wavelength, while red has the longest wavelength.

4. The seven colours contained in sunlight can often be seen in rainbows.

5. Rainbows are formed when sunlight passes through raindrops.