CBSE Class 12 Chemistry 2023 Delhi Set 1 Solved Paper

Question : 35

Total: 35

(a) Why is chemistry of actinoids complicated as compared to lanthanoids?
(b) Complete the following reaction and justify that it is a disproportionation reaction:
3MnO42−+4H+→ ______+ ______+2H2O.
(c) The given graph shows the trends in melting points of transition metals:

Explain the reason why Cr has highest melting point and manganese (Mn) a lower melting point.

Solution: 👈: Video Solution

(a) Actinoids are present below the series of lanthanoid. They are radio active in nature. To study them is more complicated as compared to lanthanoid. Second, they have variable oxidation state.
(b) 3MnO4−+4H+→2MnO4−+MnO2 +2H2O
It is disproportinoation reaction because oxidation take place in acidic medium and oxidation numbers are
MnO4‌2−=6
MnO4−=7
MnO2=4
(c)Cr=24[Ar]3d54s14
Mn=25[Ar]3d54s2
Cr has maximum number of unpaired electrons in α-orbital. So it can have maximum pairing and form bond. Number of unpaired electrons are six in Cr. But Mn has five unpaired electron in d-orbital which is less than Cr. That's why boiling point of Cr is maximum in transition metal. Mn is half filled which have extra stability and less tendency of form bonds.

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