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.
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.
Reason (R): These elements have completely filled orbitals in their ground state as well as in their common oxidation states.
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Group 12 elements (Zn, Cd, Hg) are d-block elements but NOT transition elements because their d-orbitals are completely full ($d^{10}$).
Updated On: Jul 22, 2026
- Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of the Assertion (A).
- Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of the Assertion (A).
- Assertion (A) is true, but Reason (R) is false.
- Assertion (A) is false, but Reason (R) is true.
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The Correct Option is A
Solution and Explanation
Step 1: Concept
IUPAC defines transition metals as elements whose atoms have an incomplete d-subshell, or which can give rise to cations with an incomplete d-subshell.
Step 2: Meaning
Elements of Group 12 (Zn, Cd, Hg) must be evaluated based on their d-orbital electron configurations.
Step 3: Analysis
Zinc ($3d^{10}4s^2$), cadmium ($4d^{10}5s^2$), and mercury ($5d^{10}6s^2$) possess completely filled $d$-subshells in both their atomic states and their common $+2$ oxidation states.
• Zinc, cadmium, and mercury belong to Group 12 of the periodic table.
• Their electronic configurations are: \[ Zn:3d^{10}4s^2, \] \[ Cd:4d^{10}5s^2, \] \[ Hg:5d^{10}6s^2. \]
• During ion formation, the two outermost $s$ electrons are removed first.
• Consequently, the common ions have the configurations: \[ Zn^{2+}:3d^{10}, \] \[ Cd^{2+}:4d^{10}, \] \[ Hg^{2+}:5d^{10}. \]
• Since the $d$-subshell remains completely filled, these ions contain no partially filled $d$ orbitals.
• As a result, Group 12 elements differ from typical transition elements in many of their physical and chemical properties.
• Therefore, zinc, cadmium, and mercury are generally not regarded as typical transition metals because neither their atoms nor their common ions possess incompletely filled $d$ orbitals.
Step 4: Conclusion
Because they lack partially filled d-orbitals entirely, they are not considered true transition elements. The Reason is factually true and perfectly explains the Assertion.
Final Answer: (A)
IUPAC defines transition metals as elements whose atoms have an incomplete d-subshell, or which can give rise to cations with an incomplete d-subshell.
Step 2: Meaning
Elements of Group 12 (Zn, Cd, Hg) must be evaluated based on their d-orbital electron configurations.
Step 3: Analysis
Zinc ($3d^{10}4s^2$), cadmium ($4d^{10}5s^2$), and mercury ($5d^{10}6s^2$) possess completely filled $d$-subshells in both their atomic states and their common $+2$ oxidation states.
• Zinc, cadmium, and mercury belong to Group 12 of the periodic table.
• Their electronic configurations are: \[ Zn:3d^{10}4s^2, \] \[ Cd:4d^{10}5s^2, \] \[ Hg:5d^{10}6s^2. \]
• During ion formation, the two outermost $s$ electrons are removed first.
• Consequently, the common ions have the configurations: \[ Zn^{2+}:3d^{10}, \] \[ Cd^{2+}:4d^{10}, \] \[ Hg^{2+}:5d^{10}. \]
• Since the $d$-subshell remains completely filled, these ions contain no partially filled $d$ orbitals.
• As a result, Group 12 elements differ from typical transition elements in many of their physical and chemical properties.
• Therefore, zinc, cadmium, and mercury are generally not regarded as typical transition metals because neither their atoms nor their common ions possess incompletely filled $d$ orbitals.
Step 4: Conclusion
Because they lack partially filled d-orbitals entirely, they are not considered true transition elements. The Reason is factually true and perfectly explains the Assertion.
Final Answer: (A)
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