The Cu⁺ ion is colourless and diamagnetic because its configuration is ____.
Correct answer C. [Ar]3d¹⁰
Explanation
Copper is [Ar]3d¹⁰4s¹; losing the 4s electron gives Cu⁺ = [Ar]3d¹⁰. A full d subshell has all electrons paired and allows no d-d transitions, so Cu⁺ compounds are diamagnetic and usually colourless.
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