Question

Zirconium is a transition element, but Zinc is not. Why?

• A. Both \(Zr^{3+}\) and \(Zn^{2+}\) ions are colourless and form white compounds
• B. In case of transition elements, d-orbitals are partially filled, but in Zn they are completely filled
• C. Last electron is added to 4s level in case of Zn
• D. Both Zr and Zn do not exhibit variable oxidation states

Hint:

Zn, Cd, and Hg are generally not considered transition elements because their atoms and common ions contain completely filled \(d^{10}\) configurations.

Answer 1

The Correct Option is B

Concept: According to IUPAC, a transition element is an element that has a partially filled d-subshell in its atom or in one of its common oxidation states. The presence of partially filled d-orbitals gives rise to many characteristic properties such as variable oxidation states, colored compounds, and magnetic behavior.

Step 1: Examine Zinc. Electronic configuration of zinc: \[ Zn=[Ar]\,3d^{10}4s^2 \] The \(3d\)-subshell is completely filled. For the common ion: \[ Zn^{2+}=[Ar]\,3d^{10} \] The d-orbitals remain completely filled. Hence zinc does not satisfy the transition element definition.

Step 2: Examine Zirconium. Electronic configuration: \[ Zr=[Kr]\,4d^25s^2 \] The d-subshell is partially filled. Therefore zirconium fulfills the criterion of a transition element.

Step 3: Select the correct reason. Transition elements contain partially filled d-orbitals. Zinc possesses completely filled d-orbitals. Therefore, \[ \boxed{\text{Option (2)}} \] is correct.