The correct answer is: B. Ultraviolet light.
Ultraviolet light is a type of electromagnetic radiation with a wavelength shorter than that of visible light. It is used in photolithography to expose the photoresist layer. The photoresist is a light-sensitive material that is used to create patterns on the surface of a semiconductor wafer. When exposed to ultraviolet light, the photoresist becomes hardened in the areas that are exposed to the light. The unexposed areas of the photoresist can then be washed away, leaving behind the desired pattern.
Visible light is not used in photolithography because it does not have enough energy to cause the photoresist to harden. Infra red light is also not used because it has too much energy and can cause the photoresist to harden even in the areas that are not exposed to the light. LED is not a type of light that is used in photolithography.