Which light has the shortest wavelength?

Correct answer: c violet

The light is violet when the wavelength is small, and becomes blue, green, yellow, orange and red as it grows. So violet has the shortest wavelength.

Why the other options are wrong

• a red: This is not the answer: Red has the longest wavelength, at the long end of the window (near 700 nm).
• b blue: This is not the answer: Blue comes after violet; its wavelength is a little longer than violet's.
• d yellow: This is not the answer: Yellow sits in the middle of the window, after green; its wavelength is much longer than violet's.