Solve this:
Q.5. Which one of the following ions will be colourless?
(a) $L{a}^{3+}$
(b) $N{d}^{3+}$
(c) $P{r}^{3+}$
(d) $T{i}^{3+}$

Dear Student,

The element/ion which have ​​does not have unpaired d- electrons will be colourless.

a) The electronic configurations of ₅₇La⁺³ = 1s²2s²2p⁶3s²3p⁶4s²3d¹⁰4p⁶5s²4d¹⁰5p⁶

 
b) ​​₆₀Nd⁺³:1s²2s²2p⁶3s²3p⁶4s²3d¹⁰4p⁶5s²4d¹⁰5p⁶ 4f³

c)  ₅₉Pr⁺³ : ​1s²2s²2p⁶3s²3p⁶4s²3d¹⁰4p⁶5s²4d¹⁰5p⁶ 4f²

d)​₂₂Ti⁺³ :    ​1s²2s²2p⁶3s²3p⁶4s¹3d⁰

So all ions are does not have unpaired d-electrons , so all ions are colouless.

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