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

Explanation

1) All the materials are made up of atoms and molecules. These atoms and molecules posses certain fixed energy.
2) An atom or molecule having lowest possible energy is said to be in ground state.
3) When we heat the materials the electrons of these atoms gain energy and move to excited states (higher energy state).
4) An atom of molecule in excited state can emit light to lower its energy in order to get ' stability and come back to ground state.
5) Light emitted in such process has certain fixed wavelength for one kind-of atoms.
6) The light emitted by different kinds of atoms is different because the excited states electrons will go are different. So different elements produce different flame colours.