Concept used: Enthalpy of atomisation in transition elements

Enthalpy of atomisation is the enthalpy required to convert 1 mole of atoms in the solid metallic state into gaseous atoms.

For transition elements, this quantity depends mainly on the strength of metallic bonding, which in turn depends on the number of unpaired electrons available for metallic bond formation.

General trend

• More unpaired electrons $\Rightarrow$ stronger metallic bonding
• Stronger metallic bonding $\Rightarrow$ higher enthalpy of atomisation
• Elements with completely filled subshells tend to have weaker metallic bonding and hence lower atomisation enthalpy.

Examine the given elements

(A) Fe

Electronic configuration: $\text{Fe}: [\text{Ar}]\,3d^6 4s^2$ Iron has several unpaired $d$-electrons, so metallic bonding is fairly strong. Hence, its enthalpy of atomisation is not the lowest.

(B) Cu

Electronic configuration: $\text{Cu}: [\text{Ar}]\,3d^{10}4s^1$ Copper has a filled $3d$ subshell, but still one $4s$ electron contributes to metallic bonding. Its atomisation enthalpy is lower than many transition metals, but not the minimum among the given options.

(C) V

Electronic configuration: $\text{V}: [\text{Ar}]\,3d^3 4s^2$ Vanadium has multiple unpaired electrons, leading to strong metallic bonding. Hence, it has high enthalpy of atomisation.

(D) Zn

Electronic configuration: $\text{Zn}: [\text{Ar}]\,3d^{10}4s^2$ Zinc has a completely filled $3d$ subshell and a filled $4s$ subshell. Because of this, it has very weak participation of electrons in metallic bonding compared with the others. Therefore, zinc has the lowest enthalpy of atomisation among the given options.

Conclusion

The transition element with the lowest enthalpy of atomisation is: $\boxed{\text{Zn}}$

Comparison with stored correct answer

The stored correct answer is B (Cu), but from standard NCERT/JEE trend, Zn has lower enthalpy of atomisation than Cu.

So the stored answer appears to be incorrect.