Q3
1 markMCQSection A

Which of the following is not a transition metal?

The d- and f-Block Elements
Definition of transition metals

Options

(A)Sc
(B)Ag
(C)Hg
(D)Cu
Official Answer

Correct option: (C) — Mercury (Hg).


Key idea: A transition metal must have a partially filled d-subshell in its atom or in one of its common ions.


  • Hg: [Xe] 4f14 5d10 6s2[Xe]\,4f^{14}\,5d^{10}\,6s^2; its common ion Hg²⁺ is 5d¹⁰ — a completely filled d-subshell.
  • Because neither Hg nor Hg²⁺ has an incomplete d-orbital, mercury is not a transition metal.
transition metal definitionpartially filled d-orbitalmercury Hg 5d10Hg²⁺ d10d-block elementsZn Cd Hg exceptionCu²⁺ d9 Ag²⁺ d9

Marking Scheme

  • 11 mark: correctly selecting option (C) Hg.
  • 2Accepted reason: Hg²⁺ has a completely filled 5d105d^{10} configuration.

Hint

A transition metal needs a partly filled d-subshell in the atom or an ion. Check the +2 ion of each.

Quick Oral Answer

Mercury is not a transition metal because both the atom and its common Hg²⁺ ion have a completely filled 5d105d^{10} subshell, so there is no partially filled d-orbital as the definition requires.

Analysis & Explanation

Concept:

By the IUPAC/NCERT definition, a transition element has an incompletely filled d-orbital in its ground state or in at least one of its stable oxidation states. Zn, Cd and Hg fail this test (d¹⁰ in every common state) and are treated as non-transition (only nominally 'd-block').


Checking each option:


  • (A) Sc → [Ar] 3d1 4s2[Ar]\,3d^1\,4s^2; Sc³⁺ is d⁰ but the atom has 3d¹ — genuinely transition.
  • (B) Ag → [Kr] 4d10 5s1[Kr]\,4d^{10}\,5s^1; the stable Ag²⁺ ion is 4d94d^9 (partially filled) — transition metal.
  • (D) Cu → [Ar] 3d10 4s1[Ar]\,3d^{10}\,4s^1; the common Cu²⁺ ion is 3d93d^9 (partially filled) — transition metal.
  • (C) Hg → 5d10 6s25d^{10}\,6s^2; Hg²⁺ is 5d¹⁰ (fully filled) — not a transition metal. ✅

Exam trap: Ag and Cu look like exceptions because their atoms are d¹⁰, but their ions (Ag²⁺, Cu²⁺) are d⁹, so they qualify. Hg²⁺ stays d¹⁰, so Hg is the odd one out.

Common Mistakes

  1. 1Picking Cu or Ag because their atoms are d10d^{10}, forgetting their +2 ions are d9d^9 (partially filled).
  2. 2Treating every d-block element as a transition metal — Zn, Cd, Hg are the standard exceptions.
  3. 3Confusing 'fully filled d10d^{10}' (non-transition) with 'partly filled' when writing ion configurations.

Interesting Facts

Mercury is the only metal that is liquid at room temperature (m.p. −38.83 °C), a consequence of its stable 5d106s25d^{10}6s^2 shell and relativistic contraction of the 6s orbital.

The same full-d-shell argument makes Zn, Cd and Hg poor at forming coloured ions and complexes — a hallmark that separates them from true transition metals like Cu and Sc.

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Frequently Asked Questions

Why are Zn, Cd and Hg not considered transition metals?

All three have a completely filled d10d^{10} configuration both in the atom and in their common +2 ions (Zn²⁺, Cd²⁺, Hg²⁺ are all d10d^{10}). Since the definition of a transition element requires a partially filled d-subshell in the atom or an ion, these three fail the test and are classed as d-block but non-transition metals.

Why do Cu and Ag still count as transition metals despite d¹⁰ atoms?

Although the neutral atoms of Cu ([Ar]3d104s1[Ar]3d^{10}4s^1) and Ag ([Kr]4d105s1[Kr]4d^{10}5s^1) have full d-shells, their stable ions Cu²⁺ and Ag²⁺ are d9d^9 — a partially filled d-subshell. The definition allows an element to qualify through any of its common oxidation states, so both are transition metals.