Elements with partially filled d-orbitals in atom or commonly occurring oxidation state. d-block: Groups 3-12. Show variable oxidation states, paramagnetism, color, catalytic activity, complex formation.
-- NCERT Class 12 Chemistry, Ch. 4, p. 89Transition Elements Intro
8 MCQs9-step worked example
Source: NCERT The d and f Block ElementsOfficial key: NTA-verifiedLast updated: 26 Sep 2026
Transition Elements Intro, explained for NEET
What makes an element "transition"? The definition trap NEET keeps testing.
The single most tested point from this sub-topic is the IUPAC definition of a transition element: an element whose atom has an incomplete d sub-shell or which can give rise to cations with an incomplete d sub-shell (NCERT Class 12 Chemistry Chapter 4, page 89).
Why this definition is a trap source. Students lump all d-block elements as transition elements. They are not the same set. Zinc (Zn, 3d¹⁰ 4s²), cadmium, and mercury have a completely filled d-orbital in the ground state AND in their common ionic states (Zn²⁺ is 3d¹⁰). By the IUPAC criterion, Zn is a d-block element but not a transition element. The same logic excludes Cd and Hg.
The d-block versus transition-element distinction:
- d-block = elements where the differentiating electron enters a d-orbital. Groups 3–12, four rows (3d, 4d, 5d, 6d).
- Transition element = d-block element that forms at least one ion with a partially filled d sub-shell.
Why this matters for NEET: questions ask you to identify which element from a list is NOT a transition element, or to count the number of transition elements in a given period. If you count Zn as a transition element, you lose marks.
Key facts from the NCERT entry:
- The general electronic configuration of d-block elements is (n−1)d¹⁻¹⁰ ns⁰⁻².
- The first transition series: Sc (Z = 21) to Cu (Z = 29). Note: Cu is included because Cu²⁺ has a 3d⁹ configuration (incomplete d). Zn (Z = 30) is excluded.
- Properties like variable oxidation states, coloured ions, catalytic activity, and complex formation arise from the availability of partially filled d-orbitals — but these are topics for their own dedicated lessons.
Watch-out: when a question says "d-block element," do not automatically assume "transition element." Read the options for Zn, Cd, or Hg — the examiners put them there deliberately.
Can you answer these Transition Elements Intro MCQs?
Select an option to see the explanation. Wrong answers show why your choice was tempting — and name the exact trap it exploits.
MCQ 1Easy RecallPractice
According to IUPAC, a transition element is defined as an element that:
Show answer and why every option is right or wrong
Answer: D. D is correct. The IUPAC definition requires the atom to have an incomplete d sub-shell OR to form at least one cation with an incomplete d sub-shell (NCERT Class 12 Chemistry Chapter 4, page 89).
Why A is wrong: A describes the d-block, not transition elements specifically. Zn (group 12) is d-block but not a transition element because both Zn and Zn²⁺ have completely filled 3d¹⁰.
Why B is wrong: B is incomplete — it ignores cations. Cu has a filled 3d¹⁰ 4s¹ ground state, but Cu²⁺ is 3d⁹ (incomplete), so Cu qualifies as a transition element through the cation criterion.
Why C is wrong: C is too broad. Zn²⁺ has electrons in the d-orbital (3d¹⁰) but the d sub-shell is complete, so Zn is not a transition element.
MCQ 2Easy RecallPractice
Which of the following is a d-block element but NOT a transition element?
Show answer and why every option is right or wrong
Answer: A. A is correct. Zn has the configuration [Ar] 3d¹⁰ 4s², and Zn²⁺ is 3d¹⁰ — the d sub-shell is complete in both the atom and its common cation. Zn belongs to the d-block but fails the IUPAC transition element criterion (NCERT Class 12 Chemistry Chapter 4, page 89).
Why B is wrong: B is wrong. Cu ([Ar] 3d¹⁰ 4s¹) appears to have a filled d-shell, but Cu²⁺ is 3d⁹ — incomplete. Cu qualifies as a transition element through the cation criterion.
Why C is wrong: C is wrong. Fe ([Ar] 3d⁶ 4s²) has an incomplete d sub-shell in the ground state itself. Fe is a transition element.
Why D is wrong: D is wrong. Cr ([Ar] 3d⁵ 4s¹) has an incomplete d sub-shell. Cr is a transition element.
MCQ 3Easy RecallPractice
The general electronic configuration of the outer orbitals of d-block elements is:
Show answer and why every option is right or wrong
Answer: C. C is correct. The d sub-shell fills 1 to 10 electrons, and the outermost s-orbital can hold 0, 1, or 2 electrons (NCERT Class 12 Chemistry Chapter 4, page 90). Elements like Cr and Cu have ns¹, not ns².
Why A is wrong: A is wrong. It fixes ns at 2, but several d-block elements (Cr, Cu, Mo, Ag, etc.) have ns¹ configurations due to half-filled or fully filled d-orbital stability.
Why B is wrong: B is wrong. It includes d⁰, which would mean no d-electrons at all — that does not describe a d-block element. Also fixes ns at 2.
Why D is wrong: D is wrong. The d-electrons fill the (n−1) shell, not the nth shell. The principal quantum number relationship is (n−1)d, not nd.
MCQ 4Direct ApplicationPractice
The first transition series consists of elements from Sc (Z = 21) to Cu (Z = 29). How many elements in this series are classified as transition elements by IUPAC?
Show answer and why every option is right or wrong
Answer: D. D is correct. The first transition series runs from Sc (Z = 21) to Cu (Z = 29), which is 9 elements. Zn (Z = 30) is excluded because both Zn and Zn²⁺ have a complete d¹⁰ configuration (NCERT Class 12 Chemistry Chapter 4, page 89).
Why A is wrong: A is wrong. This count includes Zn (Z = 30), which is a d-block element but not a transition element. Zn and Zn²⁺ both have 3d¹⁰ — fully filled.
Why B is wrong: B is wrong. This excludes Ni and Cu. Ni (3d⁸ 4s²) clearly has an incomplete d-shell; Cu²⁺ is 3d⁹ (incomplete). Both are transition elements.
Why C is wrong: C is wrong. This excludes Sc, but Sc ([Ar] 3d¹ 4s²) has an incomplete d sub-shell and is a transition element.
MCQ 5Direct ApplicationPractice
Cu has the electronic configuration [Ar] 3d¹⁰ 4s¹. Despite having a completely filled d sub-shell, Cu is classified as a transition element because:
Show answer and why every option is right or wrong
Answer: B. B is correct. The IUPAC definition includes elements that form cations with an incomplete d sub-shell. Cu²⁺ loses one 4s and one 3d electron, giving 3d⁹ — an incomplete d sub-shell (NCERT Class 12 Chemistry Chapter 4, page 89).
Why A is wrong: A describes why Cu has 3d¹⁰ 4s¹ instead of 3d⁹ 4s², but the anomalous configuration itself is not the reason for classification as a transition element. The definition hinges on incomplete d in the atom OR its cations.
Why C is wrong: C merely states the position of Cu in the periodic table. Being in the d-block makes Cu a d-block element, but the transition element classification requires the incomplete-d criterion, not just group membership.
Why D is wrong: D is incorrect reasoning. Not all d-block elements show variable oxidation states (Zn shows only +2), and variable oxidation states are a consequence of being a transition element, not the definition.
MCQ 6Direct ApplicationPractice
Which pair of elements are d-block elements but are NOT classified as transition elements by IUPAC?
Show answer and why every option is right or wrong
Answer: B. B is correct. Zn ([Ar] 3d¹⁰ 4s²) and Cd ([Kr] 4d¹⁰ 5s²) both have completely filled d sub-shells in the ground state, and their common cations (Zn²⁺ = 3d¹⁰, Cd²⁺ = 4d¹⁰) also have complete d sub-shells. They fail the IUPAC criterion (NCERT Class 12 Chemistry Chapter 4, page 89).
Why A is wrong: A is wrong. Cu²⁺ is 3d⁹ and Ag²⁺ is 4d⁹ — both have incomplete d sub-shells in their cationic forms. They are transition elements.
Why C is wrong: C is wrong. Sc ([Ar] 3d¹ 4s²) and Y ([Kr] 4d¹ 5s²) have incomplete d sub-shells in their ground states. They are transition elements.
Why D is wrong: D is wrong. Cr ([Ar] 3d⁵ 4s¹) and Mo ([Kr] 4d⁵ 5s¹) have incomplete d sub-shells. They are transition elements.
MCQ 7Concept TrapPractice
A student claims: 'All elements with electrons in d-orbitals are transition elements.' Which observation most directly disproves this claim?
Show answer and why every option is right or wrong
Answer: C. C is correct. Zn²⁺ has electrons in the d-orbital (3d¹⁰), yet the d sub-shell is complete. Since Zn in both atomic and cationic form has a filled d sub-shell, Zn is not a transition element — directly disproving the claim that having d-electrons automatically makes an element transitional (NCERT Class 12 Chemistry Chapter 4, page 89).
Why A is wrong: A is a valid point about d-electrons existing in non-d-block elements, but it does not address the definition of transition elements within the d-block. The student's confusion is about d-block elements, not p-block ones.
Why B is wrong: B supports the properties of transition elements but does not disprove the student's claim. It shows Fe is a transition element, which is not in dispute.
Why D is wrong: D is a subtle point — Sc³⁺ is 3d⁰, meaning it has lost all d-electrons. However, Sc in the ground state has 3d¹ (incomplete d), so Sc still qualifies as a transition element. This does not disprove the claim.
MCQ 8Concept TrapPractice
Consider the elements Sc (Z = 21), Zn (Z = 30), and Cu (Z = 29). Which statement correctly applies the IUPAC transition element definition?
Show answer and why every option is right or wrong
Answer: A. A is correct. Sc has 3d¹ (incomplete d in the ground state). Cu²⁺ has 3d⁹ (incomplete d in the cation). Both meet the IUPAC criterion. Zn and Zn²⁺ are both 3d¹⁰ (complete d), so Zn fails the criterion (NCERT Class 12 Chemistry Chapter 4, page 89).
Why B is wrong: B is wrong. Being in the d-block is necessary but not sufficient for the transition element classification. Zn is d-block but not transition because its d sub-shell is complete in both Zn and Zn²⁺.
Why C is wrong: C is wrong. Although Cu has 3d¹⁰ 4s¹ in the ground state (filled d), Cu²⁺ is 3d⁹ — an incomplete d sub-shell. The IUPAC definition considers cations too, so Cu qualifies.
Why D is wrong: D is wrong. While Sc³⁺ is 3d⁰, the definition checks the ground-state atom OR any cation. Sc in the ground state is [Ar] 3d¹ 4s² — the d sub-shell is incomplete. Sc is a transition element.
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How do you solve a Transition Elements Intro question? A worked example
- 1
Given
A list of elements from the 4th period d-block: Ti (Z = 22), Cr (Z = 24), Cu (Z = 29), Zn (Z = 30). Identify which are transition elements by IUPAC definition.
- 2
Required
Classify each element as "transition element" or "d-block but not transition."
- 3
Concept
IUPAC transition element definition: the atom has an incomplete d sub-shell, OR it forms at least one cation with an incomplete d sub-shell (NCERT Class 12 Chemistry Chapter 4, page 89).
- 4
Formula / Rule
Write the electronic configuration of the ground-state atom. If the d sub-shell is not d¹⁰, the element qualifies immediately. If it is d¹⁰, check the common cation(s).
- 5
Substitution
| Element | Ground state | d sub-shell | Cation check needed? |
|---------|-------------|-------------|---------------------|
| Ti | [Ar] 3d² 4s² | 3d² — incomplete | No (qualifies) |
| Cr | [Ar] 3d⁵ 4s¹ | 3d⁵ — incomplete | No (qualifies) |
| Cu | [Ar] 3d¹⁰ 4s¹ | 3d¹⁰ — complete | Yes |
| Zn | [Ar] 3d¹⁰ 4s² | 3d¹⁰ — complete | Yes | - 6
Calculation (cation check)
• Cu²⁺: remove 4s¹ + one 3d electron → 3d⁹ — incomplete. Cu qualifies.• Zn²⁺: remove 4s² → 3d¹⁰ — still complete. Zn does NOT qualify.
Note: atomic numbers and electron counts here are exact integers; no significant-figure considerations apply. - 7
Final answer
Ti, Cr, Cu → transition elements. Zn → d-block element, not a transition element.
- 8
Common trap
The trap is counting Zn as a transition element because it sits in the d-block (groups 3–12). The d-block label is a periodic-table position; the transition-element label requires the incomplete-d criterion. A second trap is excluding Cu because its ground state has d¹⁰ — you must check the cation.
- 9
Similar NEET-style question
"Among Sc, Fe, Ni, Zn, and Cu, how many are classified as transition elements?" (Answer: 4 — Sc, Fe, Ni, Cu. Zn is excluded.)
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What to remember before solving Transition Elements Intro questions
More in The d and f Block Elements: 3 exam traps and mistakes · 3 formulas · 3 question patterns from its other lessons.
Transition Elements Intro questions from past NEET papers
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Sources
NCERT refs: Class 12 Chemistry Chapter 4, p.89
Page numbers are the ones printed in the current NCERT textbook (2023 rationalised edition), unless marked pre-2023. The books are free at ncert.nic.in.
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