Ferrous ion changes to \(\mathrm{X}\) ion, on reacting with acidified hydrogen peroxide. The number of d-electrons present in \(\mathrm{X}\) and its magnetic moment (in B.M.) are respectively: (a) 5 and \(4.9\) (b) 4 and \(5.92\) (c) 6 and \(6.95\) (d) 5 and \(5.92\)

The oxidation state of an element in a compound reveals the number of electrons lost or gained by an atom. It’s a fundamental concept to understand chemical reactions, particularly redox processes where transfer of electrons occurs. In our exercise involving the ferrous ion, we observe how it gets oxidized. The ferrous ion, denoted as Fe²⁺, has lost two electrons compared to the neutral iron atom. During the reaction with acidified hydrogen peroxide, Fe²⁺ loses another electron and transitions into the ferric ion, Fe³⁺, indicating an increase in its oxidation state from +2 to +3. This alteration is critical as it affects the magnetic properties, which in turn play a role in the calculation of magnetic moments.

Understanding the d-electron configuration is essential in coordination chemistry. d-electrons are those that are found in the d-orbitals of transition elements. The number of d-electrons remaining after an ion has formed determines many properties, including magnetic moments. For iron (Fe), its atomic number is 26, leading to a neutral atom electronic configuration of [Ar] 3d⁶ 4s². When iron becomes Fe²⁺, it loses the two 4s electrons, resulting in a configuration of [Ar] 3d⁶. The further oxidation to produce Fe³⁺ involves losing another electron, specifically from the d-orbitals, leaving [Ar] 3d⁵. Thus, for the ferric ion, we count five d-electrons which significantly influences the ion's magnetic properties.

Ferrous ion oxidation is the process where a ferrous ion, Fe²⁺, increases its oxidation state by losing an electron to form a ferric ion, Fe³⁺. In the given exercise, the reactant acidified hydrogen peroxide serves as an oxidizing agent. Oxidizing agents pull electrons away from other substances. For students tackling this concept, envision charge like a balance scale, where adding positive charge (losing electrons) tips the scale towards a higher oxidation state. After the oxidation of the ferrous ion, we observe that it goes from having six d-electrons to five, as explained previously. In terms of chemical equations, this can be simply represented as: Fe²⁺ → Fe³⁺ + e^-.

The Bohr Magneton (\text{B.M.}) is a unit of magnetic moment named after the physicist Niels Bohr. It is a physical constant and the fundamental quantum of the intrinsic magnetic moment for an electron orbiting a nucleus. In the context of the exercise, the calculated magnetic moment provides insight into the number of unpaired d-electrons, which is closely associated with magnetic properties of the ion. The stronger the magnetic moment, the more unpaired electrons an ion has. The formula for magnetic moment is: \(\mu = \sqrt{n(n+2)}\) B.M., where n represents the number of unpaired electrons. Applying this formula to an Fe³⁺ ion with five unpaired d-electrons results in \(\mu = \sqrt{5(5+2)} = \sqrt{35} = 5.92\) B.M., which illustrates the direct relationship between the number of unpaired electrons and the magnetic moment they produce.