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(a) Give reasons for the following obser...

(a) Give reasons for the following observations:
(i) `Cu^(+)` ion is not stable in aqueous solution.
(ii) Mn (II) ion shows maximum paramagnetic character amongst the bivalent ions of first transition series.
(iii) Scandium (At. no. 21) salts are white.
(b) Describe the reactions involved in the preparation of `K_2Cr_2O_7` from chromite ore.

Text Solution

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(a) (i) `Cu^(+)` is unstable in aqueous solution due to lower hydration energy and higher reduction potential.
(ii) `Mn^(2+)` ion shows maximum para-magnetic character amongst the bivalent ions of first transition series : Configuration of `Mn^(2+)` is `3d^5 4s^2` because `Mn^(2+)` has configuration `3d^5 (##OSW_SP_CHE_XII_C08_E01_101_S01.png" width="80%"> as it has max no. of unpaired `e^(-)`, hence paramagnetic in nature.
(iii) Scandium salts are white in colour : Scandium shows only +3 oxidation state, i.e. outermost configuration `3d^(0) 4s^(0)` in which it does not have any unpaired `e^(-)`, due to which it is colourless.
(iii) Ionisation enthalpies.
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