(a)Define atomic mass unit. How is it linked with relative atomic mass?
(b) How do you know the presence of atoms if they do not exist independently for most of the elements?

Explanation

Atomic mass unit (u) is 1/12 of the mass of one atom o of C-12. Relative atomic mass of the atom of an element is the average mass of the atoms as compared to 1//12th of the mass of C-12 atom
`"Relative atomic mass of an element"=("Average mass of 1 atom of the element")/("1/12th of mass of 1 atom of C-12")`
(b)Atoms of most of the elements do not exist independently. However, they combine in specific number to form molecules or ions which we can feel and know about their presence. For example.
A molecules of `H_(2)SO_(4)`, consists of 2 atoms of H+1 atom of S+4 atoms of O
A molecules of `C_(12)H_(22)O_(11)` consists of 12 atoms of C+22 atoms of H+11 atoms of O.
Ammonium ion `(NH_(4)^(+))` consists of 1 atom of N+4 atoms of H.