State the incorrect statement from the list given below:

1. Modern atomic theory differs from Dalton's atomic theory with inference to isotopes.
2. On supplying energy initially to an atom, an electron may move from K shell to L shell of the atom.
3. An atom 'X' having equal no. of protons & neutrons in its atom, has electronic configuration-2, 8, 10.
4. Atoms of the same element having atomic mass 39 & 41 respectively, have the same electronic configuration.

An atom having equal numbers of protons and neutrons has electronic configuration 2, 8, 10.

Reason — Configuration 2, 8, 10 means total electrons =20, so protons =20. If neutrons are also 20, mass number =40. But the third shell cannot have 10 electrons before the fourth shell starts filling in the simple shell distribution used at this level. The correct configuration for 20 electrons is 2, 8, 8, 2.