Question

1. which electron - configuration notation describes an atom in an excited state? a. ar4s²3d¹⁰4p² b. ne3s²3p⁵ c. kr5s²4d¹ d. ar4s²3d⁸4p¹

Explanation:

In a ground - state atom, electrons fill orbitals in order of increasing energy following the Aufbau principle, Pauli exclusion principle, and Hund's rule. In an excited - state atom, an electron has been promoted to a higher - energy orbital. For option c, the normal filling order would have electrons filling the 5s orbital completely before starting to fill the 4d orbital. But in [Kr]5s²4d¹, it implies that an electron has been promoted from a lower - energy orbital (most likely 5p which should fill after 5s) to the 4d orbital, indicating an excited state. The other configurations follow the normal ground - state filling order.

Answer:

c. [Kr]5s²4d¹