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The d-And-f-Block Elements
Question
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How would you account for the following situations?
With 3d4 configuration, Cr2+ acts as a reducing agent but Mn3+ acts as an oxidising agent. (Atomic masses, Cr = 24, Mn = 25).

Answer

It can be explained on the basis of E° values of Cr3+ | Cr2+ (–0.4 A)
Mn3+ | Mn2+(+ 1.5 V).

On the basis of these values, it is clear that Cr2+ has a greater tendency to oxidise into Cr3+, thus it acts as reducing agent.

Cr2+(aq) → Cr3+(aq) + e–

While Mn3+ has a greater tendency to reduce into Mn2+, thus it acts as oxidising agent.
Mn3+(aq) + e– → Mn2+(aq)

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Some More Questions From The d-And-f-Block Elements Chapter

Actinoid contraction is greater from element to element than lanthanoid contraction. Why?

On what ground can you say that scandium (Z = 21) is a transition element but zinc (Z = 30) is not?

The outer electronic configuration of copper is 3d10 4s1, yet it is considered transition element. Why?

Why the melting points of transition elements are high?

Why Zn, Cd and Hg are not regarded as transition elements?

Name the first element of 3rd transition series.

Though copper, silver and gold have completely filled sets of d-orbitals yet they are considered as transition metals. Why?

Why are transition elements so named?

Why are transition elements known as d-block elements?

Write the general electronic configuration of d-block elements.