Question

Which of the following arrangements does not represent the correct order of the property stated against it?

• A. $V ^{2+} < Cr^{2+} < Mn^{2+} < Fe^{2+}$: paramagnetic behaviour
• B. $Ni^{2+} < Co^{2+} < Fe^{2+} < Mn^{2+}$ : ionic size
• C. $Co^{3+} < Fe^{3+} < Cr^{3+} < Sc^{3+}$ : stability in aqueous solution
• D. $Sc < Ti < Cr < Mn$ . number of oxidation states

Hint:

Paramagnetic property is dependent on the number of unpaired electrons.

Answer 1

The Correct Option is A

 To determine which arrangement does not represent the correct order of the property stated, let's analyze each option:

1. \(V^{2+} < Cr^{2+} < Mn^{2+} < Fe^{2+}\): Paramagnetic Behaviour

Paramagnetic behaviour depends on the number of unpaired electrons in the d-orbitals. More unpaired electrons result in greater paramagnetic character. The electron configurations are:

• \(V^{2+}\): 3d³
• \(Cr^{2+}\): 3d⁴
• \(Mn^{2+}\): 3d⁵
• \(Fe^{2+}\): 3d⁶

1. \(Ni^{2+} < Co^{2+} < Fe^{2+} < Mn^{2+}\): Ionic Size

The ionic radius generally increases with a decrease in effective nuclear charge across the series, which corresponds to this arrangement:

• \(Ni^{2+}\): Smallest
• \(Co^{2+}\)
• \(Fe^{2+}\)
• \(Mn^{2+}\): Largest

1. \(Co^{3+} < Fe^{3+} < Cr^{3+} < Sc^{3+}\): Stability in Aqueous Solution

In general, stability depends on the charge density and the stability of oxidation states. \(Co^{3+}\) tends to be more stable than \(Fe^{3+}\), followed by \(Cr^{3+}\) and \(Sc^{3+}\). Therefore, this arrangement reflects increasing stability correctly.

1. \(Sc < Ti < Cr < Mn\): Number of Oxidation States

The number of oxidation states generally increases towards the middle of the series. This trend agrees with the typical oxidation states:

• \(Sc\): +3
• \(Ti\): +2, +3, +4
• \(Cr\): +2, +3, +6
• \(Mn\): +2, +3, +4, +6, +7

The incorrect order is: \(V^{2+} < Cr^{2+} < Mn^{2+} < Fe^{2+}\): Paramagnetic Behaviour.