Transition Elements

Potassium dichromate (K₂Cr₂O₇) can be obtained from sodium chromate (Na₂CrO₄) through the following reactions:

1. 2Na₂CrO₄ + 2H⁺ → Na₂Cr₂O₇ + 2Na⁺ + H₂O
2. Na₂Cr₂O₇ + 2KCl → K₂Cr₂O₇ + 2NaCl

The general electronic configuration of f-block elements is:

(n − 2)f₁₋₁₄(n − 1)d₀₋₁ns₂

Solution:

(a) Mn³⁺ has a greater tendency to gain an electron to attain the more stable Mn²⁺ state. Cr²⁺, on the other hand, tends to lose an electron to become Cr³⁺, which is more stable. Thus, Mn³⁺ acts as an oxidizing agent while Cr²⁺ acts as a reducing agent.

(b) In actinoids, the 5f orbitals extend more into space and are less shielded, resulting in greater contraction in atomic size across the series as compared to the 4f orbitals in lanthanoids, which are better shielded.

(c) Transition metals have small atomic sizes and high charge densities. They can accommodate small atoms like H, B, C, and N in their interstitial sites, forming stable interstitial compounds that retain metallic properties.