The Cu⁺ ion forms mostly colourless compounds because it has ____.
Correct answer C. a completely filled 3d¹⁰ subshell
Topic / 35 questions
Transition Elements MCQs
Transition Elements MCQs are multiple-choice questions on the electronic structures of d-block elements and their ions, unpaired electrons, magnetic behaviour, colour and variable oxidation states. They follow the MDCAT chemistry curriculum, and every question on MCQs360 shows its correct answer instantly so you can check each configuration as you work.
- Gases 40
- Liquids 40
- Solids 40
- Chemical Equilibrium 40
- Reaction Kinetics 40
- Thermochemistry and Energetics 40
- Electrochemistry 40
- Fundamental Concepts of Chemistry 40
- Atomic Structure 39
- Chemical Bonding 39
- Alcohols and Phenols 38
- Industrial Chemistry 37
- Aldehydes and Ketones 37
- Alkyl Halides 37
- s- and p-Block Elements 37
- Chemistry of Hydrocarbons 36
- Fundamental Principles of Organic Chemistry 36
- Carboxylic Acids 36
- Transition Elements 35
- Macromolecules 35
How many unpaired electrons does the Cr³⁺ ion contain?
Correct answer D. 3
When a first-row transition metal atom forms a positive ion, electrons are removed first from the ____.
Correct answer D. 4s orbital
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How many unpaired electrons are present in the Fe³⁺ ion?
Correct answer B. 5
Which of these ions has the largest number of unpaired electrons?
Correct answer B. Mn²⁺
What is the spin-only magnetic moment of the Fe²⁺ ion?
Correct answer D. 4.90 BM
Zinc is not regarded as a typical transition element because ____.
Correct answer C. its atom and its Zn²⁺ ion both have a completely filled 3d subshell
Which of these ions is expected to be colourless in aqueous solution?
Correct answer C. Sc³⁺
What is the general outer electronic configuration of d-block elements?
Correct answer B. (n−1)d¹⁻¹⁰ ns¹⁻²
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What is the oxidation state of chromium in potassium dichromate, K₂Cr₂O₇?
Correct answer D. +6
How many d electrons are present in the Ti²⁺ ion (Ti, Z = 22)?
Correct answer B. 2
Transition elements show variable oxidation states mainly because ____.
Correct answer A. the 3d and 4s electrons are close in energy and both can be used in bonding
How many unpaired electrons are present in a ground-state chromium atom (Z = 24)?
Correct answer B. 6
What is the spin-only magnetic moment of the Cr³⁺ ion?
Correct answer A. 3.87 BM
The Cu⁺ ion is colourless and diamagnetic because its configuration is ____.
Correct answer C. [Ar]3d¹⁰
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Which ion is the most strongly paramagnetic?
Correct answer C. Mn²⁺
Which of the following ions is expected to be colourless in aqueous solution?
Correct answer D. Ti⁴⁺
The colour of most hydrated transition metal ions is due to ____.
Correct answer A. d-d electron transitions between split d orbitals that absorb visible light
Which pair of ions has the same 3d electronic configuration?
Correct answer B. Mn²⁺ and Fe³⁺
How many electrons are present in the 3d subshell of the Co³⁺ ion (Co, Z = 27)?
Correct answer C. 6
About Transition Elements MCQs
Most questions ask you to write the electronic configuration of a first-row transition element or ion, such as Cr, Cu, Fe³⁺, Co³⁺ or Ni²⁺, and count the unpaired electrons. Remember that the 4s electrons are removed before the 3d electrons when ions form, and that chromium and copper have unusual ground-state configurations. Other questions use the number of unpaired electrons to decide whether an ion is paramagnetic or diamagnetic and to calculate the spin-only magnetic moment. You will also meet the reasons for variable oxidation states, the extra stability of Fe³⁺, why Sc³⁺ salts are colourless and why zinc is not treated as a typical transition element.
Key facts to remember
- Transition elements have a partially filled d subshell in the atom or in at least one common ion.
- When first-row transition metals form ions, the 4s electrons are lost before the 3d electrons, so Fe²⁺ is [Ar]3d⁶ and Fe³⁺ is [Ar]3d⁵.
- The spin-only magnetic moment is μ = √(n(n + 2)) BM, where n is the number of unpaired electrons; Fe³⁺ and Mn²⁺ (five unpaired electrons) give about 5.92 BM.
- Transition elements show variable oxidation states because the 3d and 4s electrons have similar energies.
- Colour in transition metal compounds comes from d–d electron transitions, so ions with d⁰ (Sc³⁺) or d¹⁰ (Zn²⁺) configurations are colourless.
- Zinc is not a typical transition element because it has a full 3d¹⁰ subshell in the atom and in its only common ion, Zn²⁺.
Exams that include Transition Elements MCQs
Pakistan
- MDCAT
- ECAT
- NUMS
- AKU
- FSc boards
India
- NEET
- JEE Main
Bangladesh
- HSC
- Medical Admission Test
How to prepare for Transition Elements MCQs
- Write the configurations of Sc to Zn in a column and practise removing 4s electrons first to form ions.
- Learn the magnetic moments for 1 to 5 unpaired electrons: 1.73, 2.83, 3.87, 4.90 and 5.92 BM.
- Link d⁰ and d¹⁰ ions to colourless and diamagnetic behaviour.
- Revise the Cr and Cu exceptions together with the Atomic Structure topic.
Frequently asked questions
What does the MDCAT syllabus include in Transition Elements?
The PMDC MDCAT curriculum for Transition Elements focuses on the electronic structures of d-block elements and their ions. Questions built on this include unpaired electrons, magnetic moments, colour and variable oxidation states of first-row transition metals.
Which exams ask Transition Elements MCQs?
Transition element questions appear in MDCAT, ECAT, NUMS and AKU entry tests and in FSc board exams in Pakistan. The d-block is also a regular chapter for NEET and JEE Main in India and for HSC and medical admission tests in Bangladesh.
Why is Fe³⁺ more stable than Fe²⁺?
Fe³⁺ has the configuration [Ar]3d⁵, with a half-filled d subshell in which each of the five d orbitals holds one electron. This symmetrical arrangement is especially stable, so iron(II) compounds are readily oxidised to iron(III).
Last reviewed October 2026