Chemistry Q73 – JEE-MAIN 2025

Home Chemistry d- & f-Block ElementsQuestion #372

Among, Sc, Mn, Co and Cu, identify the element with highest enthalpy of atomisation. The spin only magnetic moment value of that element in its

+ 2

oxidation state is _______ BM (in nearest integer).

Enter Calculated Numerical Value:

Clue 1 of 3: Enthalpy of Atomisation

The enthalpy of atomisation for transition metals is related to the strength of metallic bonding, which depends on the number of unpaired electrons and the extent of d-orbital participation in bonding.

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Step 1: Identify the element with the highest enthalpy of atomisation✦ Active

The enthalpy of atomisation values for the given elements are:

Sc: 326 kJ/mol

Mn: 281 kJ/mol

Co: 430 kJ/mol

Cu: 338 kJ/mol

Among these, Cobalt (Co) has the highest enthalpy of atomisation (430 kJ/mol).

Step 2: Determine the electronic configuration of

C o^{2 +}

and the number of unpaired electrons○ Expand

The electronic configuration of Cobalt (Co) is $[A r] 3 d^{7} 4 s^{2}$ .

In the $+ 2$ oxidation state, $C o^{2 +}$ , two electrons are removed from the $4 s$ orbital.

The electronic configuration of $C o^{2 +}$ is $[A r] 3 d^{7}$ .

Filling the $3 d$ orbitals according to Hund's rule: $↑↓↑↓↑↑↑$ .

Number of unpaired electrons ( $n$ ) = 3.

Step 3: Calculate the spin-only magnetic moment○ Expand

Using the spin-only magnetic moment formula, $μ = \sqrt{n (n + 2)}$ BM:

μ = \sqrt{3 (3 + 2)} = \sqrt{3 \times 5} = \sqrt{15} BM

$\sqrt{15} \approx 3.87$ BM.

Rounding to the nearest integer, the magnetic moment is 4 BM.

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Chemistry Question 73 – JEE-MAIN 2025

Clue 1 of 3: Enthalpy of Atomisation

🧠 Full Solution Path