Assertion: Transition metal compounds are mostly paramagnetic in nature.

Reason: The paramagnetic nature increases with increase in number of unpaired electrons.

Assertion and Reason both are correct statements and reason is the correct explanation for assertion.

The correct answer is option 1. Assertion and Reason both are correct statements and reason is the correct explanation for assertion.

Let us break down the assertion and reason in detail:

Assertion: Transition metal compounds are mostly paramagnetic in nature.

Transition Metals and d-Electrons: Transition metals have partially filled d-orbitals. This means that their d-electrons are not completely paired.

Paramagnetism: A substance is paramagnetic if it has one or more unpaired electrons. Unpaired electrons have magnetic moments that align with an external magnetic field, causing the substance to be attracted to the field.

Transition Metal Compounds: Because transition metal ions usually have unpaired d-electrons, their compounds tend to be paramagnetic. For example, the iron(III) ion (Fe³⁺) has five unpaired electrons in its d-orbitals, making compounds like FeCl₃ paramagnetic.

Reason: The paramagnetic nature increases with increase in number of unpaired electrons.

Magnetic Moment: The magnetic moment of a paramagnetic substance is given by the formula \(\mu = \sqrt{n(n+2)}\) Bohr magnetons, where \(n\) is the number of unpaired electrons. This formula indicates that the magnetic moment (and thus the degree of paramagnetism) increases as the number of unpaired electrons increases.

Direct Correlation: More unpaired electrons mean a stronger magnetic moment, resulting in stronger paramagnetic behavior.

Connecting the Assertion and Reason

Why Transition Metal Compounds are Mostly Paramagnetic: Since transition metals often have unpaired electrons in their d-orbitals, their compounds exhibit paramagnetism.

The reason correctly explains the assertion because the paramagnetic nature of these compounds is directly tied to the presence and number of unpaired electrons. The more unpaired electrons present, the stronger the paramagnetic effect.

Examples to Illustrate

Iron(III) Chloride (FeCl₃): Iron in the +3 oxidation state (Fe³⁺) has five unpaired electrons. FeCl₃ is paramagnetic due to these unpaired electrons.

Manganese(II) Sulfate (MnSO₄): Manganese in the +2 oxidation state (Mn²⁺) has five unpaired electrons, making MnSO₄ paramagnetic.

Copper(II) Sulfate (CuSO₄): Copper in the +2 oxidation state (Cu²⁺) has one unpaired electron, making CuSO₄ paramagnetic, although to a lesser degree compared to Fe³⁺ or Mn²⁺ compounds.

Conclusion: Both the assertion and the reason are correct, and the reason is the correct explanation for the assertion. Transition metal compounds are mostly paramagnetic because they contain unpaired d-electrons, and the paramagnetic nature increases with the number of these unpaired electrons.