Which of the following ions is completely colourless and diamagnetic in aqueous solution? — d and f Block Elements Chemistry Question

💡 Solution & Explanation

Colour (via $d-d$ transitions) and paramagnetism require the presence of unpaired $d$ -electrons. $Sc^{3+}$ ($Z=21$) loses all three of its valence electrons to achieve an empty $3d^0$ noble gas core, making it colourless and diamagnetic.