Q7 of 70 Page 105

Which of the following oxidation state is common for all lanthanoids?

Lanthanoids show +3 oxidation state more commonly. They have a general electronic configuration of [Xe] 4fn 6s2, where it is easier to remove the 6s electrons than 4f. Removing more than one 4f electron becomes difficult and therefore the oxidation state of +3 is more common.

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5

On addition of sm 6

The magnetic nature of elements depends on the presence of unpaired electrons. Identify the configuration of transition element, which shows highest magnetic moment.

8

Which of the following reactions are disproportionation reactions?

(a) Cu+ → Cu2+ + Cu


(b) 3MnO42– + 4H+→ 2MnO4– + MnO2 + 2H2O


(c) 2KMnO4→ K2MnO4 + MnO2 + O2


(d) 2MnO4– + 3Mn2+ + 2H2O → 5MnO2 + 4H+


 9

When KMnO4 solution is added to oxalic acid solution, the decolourisation is slow in the beginning but becomes instantaneous after some time because