1s7 electronic configuration is not observed because it violates ans. Pauli’s exclusion principle Bohr’s theory Aufbau principle Hund’s rule

The electronic configuration 1s7 is not observed because it violates the Aufbau Principle.

The Aufbau Principle states that electrons occupy the lowest energy level first and then move to higher energy levels. The first energy level (1s) can only hold two electrons. Therefore, a configuration of 1s7, which places seven electrons in the first energy level, is not possible according to this principle.

It does not violate Pauli's Exclusion Principle because this principle states that no two electrons in an atom can have the same four quantum numbers, which is not related to the issue here.

It also does not violate Bohr's Theory because this theory mainly concerns the energy levels of electrons and the emission of photons, not the arrangement of electrons.

Lastly, it does not violate Hund's Rule because this rule states that electrons will singly occupy all the orbitals in a subshell before pairing up, which is also not related to the issue here.