Why are the atoms of different elements different?

“Compounds are formed when atoms of different elements combine in simple whole number ratios”. This postulate of Dalton’s theory explains-

The relative number of atoms of different elements in a compound are as follows , A = 1.33 , R = 1 and C = 1.5 . The empirical formula of the compound is

Why do different elements emit different flame colours when heated by the same non - luminous flame ?

Why are the different parts of birds different from each other ?

Why is an atom of one element different from the atoms of other elements?

IF atoms of different elements combine then……is formed.

The siotopes of neutral atom of an element differ in