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. 4Transition Elements Intro
8 MCQs9-step worked example
Source: NCERT The d and f Block ElementsPYQ coverage: NEET 2021, 2022, 2023, 2024, 2025Official key: NTA-verifiedLast reviewed: May 2026
Lesson
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 4).
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.
Practice 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:
MCQ 2Easy RecallPractice
Which of the following is a d-block element but NOT a transition element?
MCQ 3Easy RecallPractice
The general electronic configuration of the outer orbitals of d-block elements is:
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?
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:
MCQ 6Direct ApplicationPractice
Which pair of elements are d-block elements but are NOT classified as transition elements by IUPAC?
MCQ 7Concept TrapPractice
A student claims: 'All elements with electrons in d-orbitals are transition elements.' Which observation most directly disproves this 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?
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 4).
- 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.) ---
Before solving, remember these
Formulas
Spin-only magnetic moment
Magnetic moment from n unpaired electrons. 1 unpaired: 1.73 BM; 5: 5.92 BM.
| Symbol | Quantity | SI Unit |
|---|---|---|
| n | unpaired electrons | - |
| mu | magnetic moment | Bohr magneton |
Valid when
- Spin-only contribution (no orbital contribution)
- Octahedral or tetrahedral complex
Spin-only magnetic moment for transition metal
Predicts paramagnetic moment of d-block ion. n unpaired electrons in d-orbitals.
| Symbol | Quantity | SI Unit |
|---|---|---|
| n | unpaired electrons | - |
| mu | magnetic moment | BM |
Valid when
- Spin-only contribution
- Octahedral or tetrahedral complex
- First-row d-block
Common oxidation states (first-row TM)
Catalogues common stable oxidation states across first-row transition metals.
| Symbol | Quantity | SI Unit |
|---|---|---|
| OS | oxidation state | - |
Valid when
- First-row d-block
- Common (not exotic) compounds
Exam Traps & Common Mistakes
These are the exact patterns that cause wrong answers in NEET. Each trap includes when it triggers and how to avoid it.
Category: Inorganic Exception
Student assumes Mn²⁺ is the product regardless of medium. Acidic: → Mn²⁺ (5e⁻). Neutral/weakly basic: → MnO₂ (3e⁻). Strongly basic: → MnO₄²⁻ (1e⁻).
When it triggers
Question gives KMnO4 oxidation in unspecified or specific medium.
How to avoid
Always check medium. In acidic: Mn(+7) → Mn(+2). In neutral: → Mn(+4) (MnO₂). In basic: → Mn(+6) (manganate). The number of electrons (n) in Nernst calculations depends accordingly.
Root cause: concept gap
Correction
Acidic: → Mn²⁺ (5e⁻). Neutral/weakly basic: → MnO₂ (3e⁻). Strongly basic: → MnO₄²⁻ (1e⁻).
Root cause: concept gap
Correction
Lanthanoid contraction (imperfect 4f shielding) makes 5d elements similar in size to 4d. Zr/Hf, Nb/Ta, Mo/W have nearly identical chemistry.
Past Year Questions
10 questions from NEET 2021, 2022, 2023, 2024, 2025. Answers verified against NTA official keys.
NEET 2025
The correct order of decreasing basic strength of the given amines is:
1benzenamine > ethanamine > N-methylaniline > N-ethylethanamine
2N-methylaniline > benzenamine > ethanamine > N-ethylethanamine
3N-ethylethanamine > ethanamine > benzenamine > N-methylaniline
4N-ethylethanamine > ethanamine > N-methylaniline > benzenamine
NTA Answer: Option 4(final)
NEET 2024Revised key
1B and D only
2A and E only
3B and C only
4A and D only
NTA Answer: Option 1(revised_final)
NEET 2024Revised key
1d5 to d4 configuration
2d5 to d2 configuration
3d4 to d5 configuration
4d3 to d5 configuration
NTA Answer: Option 3(revised_final)
NEET 2024Revised key
The pair of lanthanoid ions which are diamagnetic is
1Ce4+ and Yb2+
2Ce3+ and Eu2+
3Gd3+ and Eu3+
4Pm3+ and Sm3+
NTA Answer: Option 1(revised_final)
NEET 2023
Which one of the following statements is correct?
1All enzymes that utilise ATP in phosphate transfer require Ca as the cofactor
2The bone in human body is an inert and unchanging substance
3Mg plays roles in neuromuscular function and interneuronal transmission
4The daily requirement of Mg and Ca in the human body is estimated to be 0.2-0.3 g
NTA Answer: Option 4(final)
NEET 2023
1B and D only
2C and D only
3B and C only
4A and E only
NTA Answer: Option 2(final)
NEET 2022
12.57
25.57
33.57
44.57
NTA Answer: Option 2(final)
NEET 2022
Gadolinium has a low value of third ionisation enthalpy because of
1high basic character
2small size
3high exchange enthalpy
4high electronegativity
NTA Answer: Option 3(final)
NEET 2022
1+6 to +5
2+7 to +4
3+6 to +4
4+7 to +3
NTA Answer: Option 2(final)
NEET 2021
Tritium, a radioactive isotope of hydrogen, emits which of the following particles? (β–)
1Neutron (n)
2Beta (α) (γ)
3Alpha
4Gamma
NTA Answer: Option 2(final)
How NEET usually asks this
Recurring question shapes from past papers. Each pattern shows why wrong options look tempting.
Use KMnO4 or K2Cr2O7 in acidic/neutral/basic medium for oxidation. Different products by medium.
InterpretationMedium
Common distractors
uses acidic formula in basic medium
Assumes Mn²⁺ regardless of medium
Effect of lanthanoid contraction on properties of 4d/5d transition metals. Closer atomic/ionic radii, similar properties (Zr/Hf, Nb/Ta).
RecallEasy
Common distractors
predicts large difference due to period shift
Expects 5d to be much larger than 4d
Predict highest stable oxidation state for transition metal. Mn: +7 in MnO4-. Fe: +3 stable. Cu: +2.
InterpretationMedium
Common distractors
misses d0 d10 stability
Doesn't account for closed-shell stability
Sources
NCERT refs: Class 12 Chemistry Chapter 4, p.4
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