Question

What are the mass number of first 20 elements ?​

Answer 1

Answer:

The atomic mass (mₐ or m) is the mass of an atom. Although the SI unit of mass is the kilogram (symbol: kg), atomic mass is often expressed in the non-SI unit atomic mass unit (AMU) or unified mass (u) or dalton (symbol: Da), where 1 AMU or 1 u or 1 Da is defined as 1⁄12 of the mass of a single carbon-12 atom, at rest. The protons and neutrons of the nucleus account for nearly all of the total mass of atoms, with the electrons and nuclear binding energy making minor contributions.