An electron microscope would be used for if
a)a sample needed to appear lighter
b) a sample was too small to be with an optical microscope
c) details of cell structures needed to be distinguished

Electron microscope would be used for if,

C) details of cell structures needed to be distinguished.

Explanation:

The general principal of electron microscopy is analogous to light microscopy except that it uses electrons to analyse the specimen instead of light.Electron microscopy focuses a beam of electron on the target sample and records the difference in absorption by different surfaces.Electron microscopy is used to get the detailed structure of cells and surface features of various viruses and bacteria.However, it is not possible to view living biological samples through electron microscope because high velocity electron have immense energy to kill living cells.These samples are thus, fixed and then viewed.