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Question

(i) With reference to structural variability and chemical reactivity, write the difference between lanthanoids and actinoids.
(ii) Name a member of the lanthanoid series which is well known to exhibit +4 oxidation state.
(iii) Complete the following equation:
MnO4+8H++5e
(iv) Out of Mn3+ and Cr3+, which is more paramagnetic and why?
(atomic number : Mn=25,Cr=24)

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Solution

(i) The difference between lanthanoids and actinoids with respect to their structural variability and chemical reactivity are as follows:
a) Actinoids are radioactive, while lanthanoids are not radioactive.
b) The ionisation enthalpies of the early actinoids are lower than those of the early lanthanoids. Actinoids show the oxidation state from +3 (most common) to +7, while lanthanoids show the oxidation state from +3 up to +7.
c) Actinoids are more reactive and have more complex magnetic properties than lanthanoids.
(ii) Cerium is a lanthanoids element that is known to exhibit the oxidation state of +4.
(iii) The complete equation is as follows :
MnO4+8H++5eMn2++4H2O
(iv) Mn2+ is more paramagnetic because it has more number of unpaired electrons than Cr3+ (5u.e>3u.e).

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