Question

Assertion (A): Zinc, cadmium and mercury are not considered as transition elements.
Reason (R): These elements have completely filled orbitals in their ground state as well as in their common oxidation states.

• A. Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of the Assertion (A).
• B. Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of the Assertion (A).
• C. Assertion (A) is true, but Reason (R) is false.
• D. Assertion (A) is false, but Reason (R) is true.

Hint:

Group 12 elements (Zn, Cd, Hg) are d-block elements but NOT transition elements because their d-orbitals are completely full ($d^{10}$).

Answer 1

The Correct Option is A

Step 1: IUPAC definition of transition elements.
According to IUPAC, a transition element is one whose atom or cation has an incompletely filled d subshell. This is the key criterion for classification.
Step 2: Ground-state d-configurations.
$Zn~[3d^{10}4s^2]$, $Cd~[4d^{10}5s^2]$, $Hg~[5d^{10}6s^2]$ — all three have fully filled d subshells in the neutral atom.
Step 3: Common ion configurations.
In the common $+2$ oxidation state: $Zn^{2+}$ is $3d^{10}$, $Cd^{2+}$ is $4d^{10}$, $Hg^{2+}$ is $5d^{10}$. The d subshell is still completely filled, so the IUPAC criterion is not met in any oxidation state.
Step 4: Evaluate the assertion-reason pair.
Assertion (A) is true. Reason (R) correctly states that d-subshells remain fully filled in both ground state and common oxidation states. R is the correct explanation for A.
\[ \boxed{(A)} \]