firstly you need to know what an isotope is - it is an atom of an element which has a different number of neutrons than normal but the same number of protons and electrons.
because neutrons add mass an isotope can be more or less in weight than a normal atom of that element this means that you have a relative isotopic mass which is the mass of an atom of a particular isotope compared to Carbon 12
because atoms of an element can vary in mass due to isotopes we must take this into account when saying what the relative atomic mass is of an element
The relative atomic mass- is the weighted average mass of a atoms of an element compared to carbon 12
the word weighted in the definition refers to the fact that there are isotopes by weighted it means that the mass leans towards the weight which is most common of all of the isotopes so that these masses are shown equally
for example Cl 35 and Cl 37- the RAM of Cl is…