Which type of electromagnetic waves are used in an optical microscope? Why?

(N/A) An optical microscope uses visible light waves.
The wavelength of visible light is in the range of $4000 \; \mathring{A}$ to $7000 \; \mathring{A}$ (where $1 \; \mathring{A} = 10^{-10} \; m$).
Due to the wave nature of light,an optical microscope can resolve objects or measure dimensions that are comparable to the wavelength of the light used.
However,it cannot be used to resolve dimensions significantly smaller than the wavelength of visible light (e.g.,atomic or molecular scales like $10^{-10} \; m$),as the diffraction limit prevents higher resolution.