The light of one single color is called:
(A) Monochromatic light
(B) Bi-chromatic light
(C) Tri-chromatic light
(D) Poly-chromatic light

Hint Generally, lights are subjected to undesirable lights interacting on them. So they actually contain lights of varied frequency. A monochromatic light is one that contains photons of only 1 frequency. They are generally used in experiments where we need some particular type of light.

Step by step solution
A monochromatic light is basically an electromagnetic radiation consisting of a beam of photons all travelling at the same frequency, i.e. the frequency is single and constant throughout. The light which has a single characterizing frequency will exhibit only one color.
Normal white light or sunlight is a mixture of several colors of lights ranging from \[4 \times {10^{14}}\] to \[8 \times {10^{14}}\] Hertz. Therefore, normal white light or sunlight is not monochromatic.

Therefore, option (A) is correct.
An example of monochromatic light source is laser, it is considered to be the best monochromatic light source as it provides strictly monochromatic light of a single frequency. A sodium lamp is another example of a monochromatic light source, however it has two frequencies but the difference between them is minimal and the light is strictly yellow in color.

Note The Greek prefix ‘Mono’ refers to one single quantity, ‘Bi’ refers to two, ‘Tri’ refers to three, ‘Poly’ refers to multi or many. Also, the Greek word ‘chrome’ refers to color. So, a monochromatic light is a light of one single color.