The species with no electron in the 3d-orbital is

Analyze the question: We need the species whose 3d orbital is empty (0 electrons).

Concept: Write the electron configuration of each neutral atom, then remove electrons for cations. For transition metals, electrons are removed first from the 4s orbital, then from 3d.

Solution:

• A. Zn²⁺: Zn is [Ar] 3d¹⁰ 4s². Removing 2 electrons from 4s gives [Ar] 3d¹⁰. It has 10 electrons in 3d.
• B. Sc³⁺: Sc is [Ar] 3d¹ 4s². Removing 3 electrons (2 from 4s, 1 from 3d) gives [Ar]. The 3d orbital has 0 electrons.
• C. Cu: Cu is [Ar] 3d¹⁰ 4s¹. It has 10 electrons in 3d.
• D. Mn: Mn is [Ar] 3d⁵ 4s². It has 5 electrons in 3d.

Answer: Only Sc³⁺ has an empty 3d orbital, since it has the same configuration as argon (1s² 2s² 2p⁶ 3s² 3p⁶).

Tip: A transition metal ion that has lost all of its valence electrons (for example Sc³⁺, Ti⁴⁺) becomes isoelectronic with a noble gas, so its d-orbitals are empty. Always remove the 4s electrons first, then the 3d electrons.