Ferrous ion changes to X ion, on reacting with acidified hydrogen peroxide. The number of d-electrons present in X and its magnetic moment (in B.M.) are respectively:

5 and 5.92

The correct answer is option 4. 5 and 5.92.

When the ferrous ion \((Fe^{2+})\) reacts with acidified hydrogen peroxide \((H_2O_2)\), it undergoes oxidation to form a new species, denoted as X. This oxidation converts \(Fe^{2+}\) to \(Fe^{3+}\).

The electronic configuration of \(Fe^{2+}\) is \([Ar] 3d^6\), which means it has 6 d-electrons. Upon oxidation to \(Fe^{3+}\), one electron is lost, resulting in 5 d-electrons in the X ion.

The magnetic moment of an ion can be calculated using the formula:

Magnetic Moment, \(\mu = \sqrt{n(n+2)}\), where n represents the number of unpaired electrons.

In this case, the number of unpaired electrons is 5. Plugging this value into the formula, we get:

Magnetic Moment, \(\mu = \sqrt{5(5 + 2)} = \sqrt{35} \approx 5.92 B.M\)

Therefore, the correct answer is (4) 5 and 5.92, representing the number of d-electrons in X and its magnetic moment, respectively.