The electron configuration of a ground-state Co atom is A) [Ar]4s²3d⁷. B) 1s²2s²2p⁶3s²3d⁹. C) [Ne]3s²3d⁷. D) [Ar]4s¹3d⁵. E) [Ar]4s²4d⁷.

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The electron configuration of a ground-state Co atom is [Ar]4s²3d⁷. This is because Co has 27 electrons, and the Aufbau principle states that electrons fill orbitals in order of increasing energy. The 1s, 2s, 2p, 3s, and 3p orbitals are all filled before the 3d orbitals, so the 3d orbitals are the first to be filled in the Co atom. The 3d orbitals can hold a maximum of 10 electrons, so the Co atom has 7 electrons in its 3d orbitals. The 4s orbital is the next highest energy orbital, so the Co atom has 2 electrons in its 4s orbital.

The Electron Configuration of a Ground-State Co Atom Is