A green chromium compound (A) on fusion with alkali gives a yellow compound (B) which on acidification gives an orange coloured compound (C). ‘C’ on treatment with NH₄Cl gives an orange coloured product (D), which on heating decomposes to give back (A). Identify A, B, C and D. Write equations for reactions.

(a)

(i) The ionisation energy gradually increases with increase in atomic number along a given transition series. So transition elements tend to be unreactive with increase in atomic number in a series.

(ii) In transition elements, the energies of (n – 1) d-orbitals and ns orbitals are very close. Hence electrons from both can participate in bonding. The principal oxidation state of lanthanoids is +3.




The equation for reactions are as follows: