Question

Assertion (A): Transition elements have higher enthalpies of atomization.
Reason (R): Large number of unpaired electrons present in transition elements facilitate strong interatomic interaction and strong bonding between atoms.

• A. Both (A) and (R) are correct and (R) is the correct explanation of (A)
• B. Both (A) and (R) are correct and (R) is not the correct explanation of (A)
• C. (A) is correct and (R) is incorrect
• D. (A) is incorrect and (R) is correct

Hint:

For transition elements, a larger number of unpaired \(d\)-electrons generally leads to stronger metallic bonding, higher enthalpy of atomization, and higher melting and boiling points.

Answer 1

The Correct Option is A

Step 1: Analyze Assertion (A).
Enthalpy of atomization is the energy required to separate one mole of atoms from a solid metallic crystal into gaseous atoms. Transition elements generally possess high enthalpies of atomization because they exhibit very strong metallic bonding.
Therefore, Assertion (A) is correct.

Step 2: Understand metallic bonding in transition elements.
In transition metals, both \((n-1)d\) electrons and \(ns\) electrons participate in metallic bonding. A larger number of unpaired electrons results in greater overlap between atomic orbitals and stronger metal-metal interactions.

Step 3: Analyze Reason (R).
Transition elements often contain several unpaired electrons in their \(d\)-orbitals. These unpaired electrons contribute significantly to strong interatomic attraction and strong metallic bonding.
Hence, Reason (R) is correct.

Step 4: Establish the relationship between A and R.
Because of the strong metallic bonding arising from the participation of many unpaired \(d\)-electrons, \[ \text{Strength of metallic bonding} \uparrow \] which leads to \[ \text{Enthalpy of atomization} \uparrow \] Therefore, the reason correctly explains why transition elements have high enthalpies of atomization.

Step 5: Final conclusion.
Both Assertion (A) and Reason (R) are correct, and Reason (R) is the correct explanation of Assertion (A).
\[ \boxed{\text{Both (A) and (R) are correct and (R) is the correct explanation of (A)}} \] Hence, option (1) is correct.