How are light microscopes different from electron microscopes?
electron microscopes can view the internal part of a cell, while light microscopes view the surface of a cell.
electron microscopes' specimens can be stained for contrast, while light microscopes' specimens appear black and white.
electron microscopes are used for dissections, while compound light microscopes are not
electron microscopes use electron beams and electromagnetic lenses, while compound light microscopes use light and ocular and objective lenses.

the relative atomic mass of an element is the mass of one atom of that element, relative to 1/12th of the mass of a  1212c atom. to convert to an absolute mass in kg, it is necessary to multiply by  1.661×10−271.661×10−27.

the relative atomic mass is roughly equal to the number of neutrons, plus the number of protons, in the nucleus of the atom.

for elements with more than one stable isotope (different types of nucleus with different numbers of neutrons but the same number of protons), the quoted mass is usually the average mass, weighted by the relative abundance of the different isotopes.