A) all these are colourless
B) all these are coloured
C) only\[\text{N}{{\text{i}}^{\text{2+}}}\] is coloured and\[\text{Z}{{\text{n}}^{\text{2+}}}\] and \[\text{C}{{\text{r}}^{\text{3+}}}\]are colourless
D) only \[\text{Z}{{\text{n}}^{\text{2+}}}\] is colourless and \[\text{N}{{\text{i}}^{\text{2+}}}\]and \[\text{C}{{\text{r}}^{3+}}\] are coloured
Correct Answer: D
Solution :
The ions having unpaired electrons are coloured. \[Z{{n}^{2+}}=1{{s}^{2}},2{{s}^{2}},2{{p}^{6}},3{{s}^{2}},3{{p}^{6}},4{{s}^{o}},3{{d}^{10}}\] \[C{{r}^{3+}}=1{{s}^{2}},2{{s}^{2}},2{{p}^{6}},3{{s}^{2}},3{{p}^{6}},4{{s}^{0}},3{{d}^{3}}\] \[N{{i}^{2+}}=1{{s}^{2}},2{{s}^{2}},2{{p}^{6}},3{{s}^{2}},3{{p}^{6}},4{{s}^{0}},3{{d}^{8}}\] \[\therefore \] Only\[Z{{n}^{2+}}\] is colourless as it has all electron paired. \[\therefore \]\[C{{r}^{3+}}\]and\[N{{i}^{2+}}\]are coloured due to the presence of unpaired electrons.
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