How many atoms of oxygen in 4 molecules of HNO_3

Express these numbers in atomic mass units ("u"). Note the amounts of atoms of all the component in HNO3, which are 1 atom of Hydrogen, 1 atom of Nitrogen and 3 atoms of Oxygen. ( I asked my teacher about this too)

Explanation:

answer: atomic mass was originally used to arrange elements on the periodic table, but is no longer used to organize the modern version.

explanation:

originally atomic mass was used to arrange elements on the periodic table from left to right in a row. each column then shows similar properties of elements of a group.

in modern periodic table, the atoms are arranged in increasing atomic number. as atomic number represents the number of protons in an atom which is unique for every atom.