Which isotope of C is used for expressing relative atomic masses of element ?

Define atomic mass of an element.

What were the units used for expressing atomic masses of elements initially ?

Which unit is used for expressing molecular masses ?

What are the units used to express the atomic radius ?

How will you express gram atomic mass in terms of moles?

The atomic mass of an element is the weighted average of the atomic masses of different isotopes of that element .This explains,why atomic masses of many elements show large departures from integer values.However ,even if we consider msases of individual isotpes,they are not strictly integer multiples of the mass of a hydroen atom.How do yo account for this fact?

Which isotope of carbon is used as a standard reference to express atomic masses ?

Which unit is used now-a-days to express atomic masses ?