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Question
Which of the following cations are coloured in aqueous solutions and why ?
Sc3+, V3+, Ti4+, Mn2+ (At. Nos. Sc = 21, V = 23, Ti = 22, Mn = 25)
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Solution
The color of cations is dependent on the number of unpaired electrons present in d-orbital. The electronic configuration of the following cations is as follows:
Sc (Atomic number 21) = 3d1 4s2 and Sc3+ = 3d0 4s0. As d-orbital is empty, it is colourless.
V (Atomic number 23) = 3d3 4s2 and V3+ = 3d2 4s0. As d-orbital is having 2 unpaired electrons, it undergoes d-d transition and shows green colour.
Ti = (Atomic number 22) = 3d2 4s2 and Ti4+ = 3d0 4s0. As d-orbital is empty, it is colourless.
Mn = (Atomic number 25) = 3d5 4s2 and Mn2+ = 3d5 4s0. As d-orbital is having 5 unpaired electrons, it shows pink color.
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