Answer : 3. "white light"
Explanation :

Answer: C) white light Explanation: As far as the rate of photosynthesis is concerned, it is fastest in white light making the rate of photosynthesis maximum. After White, We Have Violet Light Where Photosynthesis Occur To A Higher Extent as It Has The Shortest Wavelength Hence Has The Max Energy.   So The Order Is  ::  white>violet>blue.