Question

difference between relative atomic mass and relative molecular mass

Answer 1

Just what it sounds like it is. The RAM is for the atom (as in C, H, O, Cl, etc) while the RMM is for the molecule (as in C, H2, O2, Cl2, C2H6, etc). Obviously, the RA< and the RMM are the same for monoatomic atoms such s C, He, Ne, etc.