NEET Practice Questions (MCQs) with Answers & Solutions

The ion $Ti^{4+}$ cannot show d-d transitions because it has an empty d-orbital (3d^0 configuration). D-d transitions require electrons in the d-orbitals to move between different d-orbital energy levels, but since $Ti^{4+}$ has no electrons in its d-orbitals, such transitions cannot occur.

The electronic configuration $(n-1)d^5 ns^2$ can show the highest oxidation state. This is because elements with this configuration have a half-filled d-subshell, which is relatively stable and can lose more electrons to achieve a higher oxidation state. An example is manganese (Mn) with configuration $3d^5 4s^2$, which can exhibit an oxidation state of +7.

Potassium dichromate ($K_2Cr_2O_7$) is commonly used to oxidize ferrous ions (Fe^2+) to ferric ions (Fe^3+) in an acidic medium. It acts as a strong oxidizing agent in various chemical reactions.

Cerium oxide ($CeO_2$) is commonly used as a pigment due to its excellent properties such as high stability and resistance to heat. It is often used in ceramics and glass to provide a yellow color.

The stability of an oxidation state in lanthanide elements depends on the combined effect of hydration energy and ionization energy. These factors determine how easily an ion can form and remain stable in a solution.

The element with the electronic configuration $[Ar] 3d^8$ for its $M^{2+}$ ion is Nickel (Ni). The atomic number of Nickel is 28. When it loses two electrons to form $Ni^{2+}$, the configuration becomes $[Ar] 3d^8$.

Among the lanthanides, Europium (Eu) is known to show both +2 and +3 oxidation states. This is because the +2 oxidation state of Eu has a stable half-filled f-orbital configuration \(4f^7\\).

Lanthanide contraction is observed due to an increase in effective nuclear charge. As we move across the lanthanide series, electrons are added to the 4f orbitals, which do not shield the nuclear charge effectively, leading to a stronger attraction between the nucleus and the outer electrons, thus causing a contraction in atomic and ionic sizes.

In the f-block elements, also known as the lanthanides and actinides, the atomic volume decreases with an increase in atomic number. This phenomenon is due to the lanthanide contraction, where the addition of electrons to the 4f orbitals results in poor shielding, leading to an increase in the effective nuclear charge and a consequent decrease in atomic and ionic radii.