Question

Which of the following elements of the 3d series of transition elements has the lowest \(\Delta_{a} H^\circ\)?

• A. Sc
• B. Cr
• C. Cu
• D. Zn

Hint:

The elements with a completely filled d-subshell, such as Zn, exhibit greater stability and lower enthalpy change, while other transition elements with partially filled d-subshells tend to have higher enthalpy changes.

Answer 1

The Correct Option is D

\(\Delta H^\circ\) refers to the enthalpy change or heat of formation for a particular element in its standard state. For transition elements, the enthalpy change is affected by the electron configuration, the stability of the element, and its ionization energy.
- Scandium (Sc) and chromium (Cr) have relatively high ionization energies and enthalpy changes.
- Copper (Cu) has a relatively stable electron configuration due to its completely filled d-subshell, making it less reactive and having a moderate \(\Delta H^\circ\).
- Zinc (Zn), on the other hand, has a completely filled 3d subshell and a stable electron configuration, making it the least reactive and having the lowest enthalpy change among the 3d transition elements. This is why Zn has the lowest \(\Delta H^\circ\).
Thus, the correct answer is Zn.