NCERT MCQ Solutions for Class 12 Chemistry Chapter 4 The d and f Block Elements

The d-block of the periodic table contains the elements of groups 3–12.

Zn, Cd and Hg have full d¹⁰ configuration in their ground state and common oxidation states, hence they are not regarded as transition metals. The IUPAC definition requires an incomplete d subshell in the neutral atom or its ions.

The general electronic configuration of outer orbitals as (n−1)d¹⁻¹⁰ ns¹⁻², except for Pd.

Cr is an exception due to the stability of the half-filled d subshell, resulting in the 3d⁵ 4s¹ configuration instead of 3d⁴ 4s².

The high melting points to the involvement of a greater number of electrons from (n−1)d in addition to the ns electrons in the interatomic metallic bonding.

The regular decrease in atomic radii from lanthanum to lutetium as Lanthanoid contraction.

The net result of the lanthanoid contraction is that the second and third d series exhibit similar radii (e.g., Zr and Hf).

Manganese exhibits all the oxidation states from +2 to +7, the greatest number in the first series.

The opposite of the p-block trend is true for d-block groups; heavier members favour higher oxidation states (e.g., Mo(VI) and W(VI) are more stable than Cr(VI)).

Paramagnetism arises from unpaired electrons, and the magnetic moment (calculated using the spin-only formula) is determined by the number of unpaired electrons.

The ‘spin-only’ formula μ = √(n(n + 2)), where n is the number of unpaired electrons.

The colour to the absorption of light corresponding to the energy required to excite an electron from a lower energy d orbital to a higher energy d orbital.

Comparatively smaller ionic sizes, high ionic charges and the availability of d orbitals for bond formation as reasons for complex formation.

Characteristics like high melting points (higher than pure metals), being very hard, retaining metallic conductivity and being chemically inert.

Mischmetall as a well-known alloy consisting of about 95% lanthanoid metal.

Dichromates are prepared from chromate, obtained by fusing chromite ore with sodium or potassium carbonate in free access of air.

The oxidizing action in acidic solution is represented by the half-reaction:
Cr₂O₇²⁻ + 14H⁺ + 6e⁻ → 2Cr³⁺ + 7H₂O.

KMnO₄ is commercially prepared by alkaline oxidative fusion of MnO₂ (pyrolusite ore).

The f-block consists of elements where 4f (lanthanoids) and 5f (actinoids) orbitals are progressively filled.

The actinoid contraction is greater from element to element in the series compared to lanthanoid contraction, resulting from poor shielding by 5f electrons.