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

The concept of oxidation states in transition metals is pivotal for understanding their chemical behavior. Transition metals are elements found in groups 3 to 12 of the periodic table and are characterized by having partially filled d-subshells. These elements can exhibit a wide range of oxidation states, which are essentially the charges that an atom would have if all bonds were ionic.

Oxidation states are important because they determine how a transition metal can bond with other elements and what kind of compounds it can form. Oxidation changes often lead to variations in color, magnetic properties, and reactivity. For instance, in the exercise, the ferrous ion, denoted as Fe^(2+), reacts with acidified hydrogen peroxide and is oxidized to the ferric ion, Fe^(3+). This change from +2 to +3 is a shift in the oxidation state by one unit, which results in a different d-electron configuration and magnetic moment.

The d-electron configuration refers to the arrangement of electrons in the d-subshell of transition metals. The number of electrons in the d-subshell is critical for determining the chemical and physical properties of the metal. Importantly, the configuration influences the magnetic moment and the overall stability of the metal ion.

In our example, the ferrous ion has a d^6 configuration, which means there are six electrons in the d-subshell. When it is oxidized to the ferric ion, it loses one electron, changing its configuration to d^5. This d^5 configuration is significant because it represents a half-filled d-subshell, which is often more stable due to the symmetry and exchange energy. These subtleties in electron configuration play a crucial role in the magnetic moments and the way in which transition metal ions interact with each other and form coordination compounds.

The magnetic properties of coordination compounds are closely linked to the d-electron configuration of the central transition metal ion. Magnetic moment is a vector quantity that is related to the magnetism of the atom or ion and is driven by the orbital and spin angular momentum of electrons.

In coordination compounds, unpaired electrons in the d-orbitals of the metal ion create a magnetic field, which contributes to the overall magnetic moment of the compound. For instance, the ferric ion (Fe^(3+)) with a d^5 configuration has five unpaired electrons, each contributing to the magnetic moment. The formula \(\mu = \sqrt{n(n+2)}\), where \(n\) is the number of unpaired electrons, allows us to calculate the magnetic moment. In paramagnetic compounds like our ferric ion case, the higher the number of unpaired electrons, the greater the magnetic moment, leading to stronger magnetic properties.