The correct answer is Option C: Pauli exclusion principle.

The Pauli exclusion principle states that no two electrons can have the same set of four quantum numbers. In simpler terms, it means that each orbital can hold a maximum of two electrons, and these two electrons must have opposite spins. The quantum numbers that define an electron's state in an atom include the principal quantum number (n), the angular momentum quantum number (l), the magnetic quantum number (m_l), and the spin quantum number (m_s).

The electronic configuration given as 1s⁷ would imply trying to place seven electrons into the 1s orbital. However, an s orbital can accommodate a maximum of two electrons, provided they have opposite spins. This arrangement means that trying to place more than two electrons in the 1s orbital would indeed violate the Pauli exclusion principle because it would require at least some of these electrons to have the same set of quantum numbers, which is not possible.

Let's briefly address why the other options do not fit:

Option A: Heisenberg uncertainty principle concerns itself with the limit to which the position and momentum (or velocity) of an electron can be known simultaneously. This principle does not directly relate to the issue of how many electrons can occupy a given orbital or energy level.

Option B: Hund's rule deals with the distribution of electrons across orbitals of the same energy (degeneracy). It states that electrons will fill each degenerate orbital singly before any orbital gets a second electron, and all singly occupied orbitals will have electrons with the same spin. This rule does not apply to the violation seen in the 1s⁷ configuration.

Option D: Bohr's postulate of stationary orbits pertains to the quantum condition that electrons orbit the nucleus in certain stable orbits without radiating energy. This principle is more historical and foundational to quantum theory and does not address the occupancy limits of orbitals or the exclusion principle directly.

Therefore, the concept violated by having a 1s⁷ configuration is the Pauli exclusion principle (Option C), as this configuration suggests more than two electrons attempting to occupy the same quantum state within the 1s orbital, which is not permissible.