Read the passage carefully and answer the questions.

Nearly all the transition elements display typical metallic properties such as high tensile strength, ductility, malleability, high thermal and electrical conductivity and metallic lustre. The transition metals (with the exception of Zn, Cd and Hg) are very hard and have low volatility. Their melting and boiling points are high. They have high enthalpies of atomization. Ions of the same charge in a given series show progressive decrease in radius with increasing atomic number. However, the variation within a series is quite small. The filling of 4f before 5d orbital results in a regular decrease in atomic radii called Lanthanoid contraction which essentially compensates for the expected increase in atomic size with increasing atomic number. The net result of the lanthanoid contraction is that the second and the third d series exhibit similar radii (e.g., Zr 160 pm, Hf 159 pm) and have very similar physical and chemical properties. There is an increase in ionisation enthalpy along each series of the transition elements from left to right. The first ionisation enthalpy, in general, increases, but the magnitude of the increase in the second and third ionisation enthalpies for the successive elements, is much higher along a series. One of the notable features of a transition elements is the great variety of oxidation states these may show in their compounds.

In the first transition series of elements (Sc to Zn), which element show least enthalpy of atomization?

Zn

The correct answer is Option (4) → Zn

Enthalpy of atomization ($ΔH_{\text{atom}}$​) is the energy required to convert 1 mole of a solid metal into gaseous atoms.

• It depends on the number of unpaired d-electrons, as more unpaired electrons → stronger metallic bonding → higher $ΔH_{\text{atom}}$​.
• In the first transition series:

• Zn has completely filled 3d¹⁰ orbital, resulting in weak metallic bonding.
• Therefore, Zn has the lowest enthalpy of atomization.

 Correct answer: Zn