MDCAT Chemistry chapter 12: Chemistry · Transition elements MCQs with answers

By Team Megalecture · Updated 4 Nov 2026

37 exam-style questions on Chemistry · Transition elements, each with the answer and a short explanation. Ten of them are below to try. The chapter test draws ten fresh questions each time and is marked the moment you finish, with your score by topic.

37 questions · 2 topics · 10 per test

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What chapter 12 covers

Ten Chemistry · Transition elements questions with answers

Try each one, then open the answer. These ten stay the same; the test draws new ones every time.

1. Which ion has the most unpaired electrons, and so is the most strongly paramagnetic? (Z: Mn 25, Fe 26, Ni 28, Cu 29)

  1. A
    Fe2+
  2. B
    Ni2+
  3. C
    Mn2+
  4. D
    Cu2+
Show answer

Answer: C. Mn2+ is 3d5: one electron in each of the five d orbitals, all unpaired (Hund's rule). Fe2+ (3d6) has four, Ni2+ (3d8) two and Cu2+ (3d9) one.

2. Sodium hydroxide solution is added to an orange solution of potassium dichromate. The solution turns

  1. A
    green, as chromium(III) ions are formed
  2. B
    a deeper orange, as more dichromate forms
  3. C
    colourless, as the chromium is reduced
  4. D
    yellow, as chromate ions are formed
Show answer

Answer: D. Cr2O72− + 2OH− ⇌ 2CrO42− + H2O: the alkali removes H+ and shifts the equilibrium to yellow chromate, while adding acid shifts it back to orange dichromate. Green Cr3+ would need a reducing agent.

3. Zinc is not regarded as a typical transition element because

  1. A
    its atom and its Zn2+ ion both have a full 3d subshell
  2. B
    its atom has no electrons at all in the 3d subshell
  3. C
    it shows a wide range of variable oxidation states
  4. D
    its compounds are all strongly coloured and paramagnetic
Show answer

Answer: A. Zn is [Ar] 3d10 4s2 and forms only Zn2+ ([Ar] 3d10), so neither has a partly filled d subshell. Its compounds are therefore white and diamagnetic, and it shows only the +2 state; Zn, Cd and Hg are called non-typical transition elements.

4. Which ion is diamagnetic (has no unpaired electron)?

  1. A
    Cu2+
  2. B
    Fe3+
  3. C
    Ti3+
  4. D
    Cu+
Show answer

Answer: D. Cu+ is [Ar] 3d10, with every electron paired. Cu2+ (3d9) and Ti3+ (3d1) each have one unpaired electron and Fe3+ (3d5) has five, so they are paramagnetic.

5. The complex ion [Fe(CN)6]3−, with six ligands around the metal ion, has the shape

  1. A
    hexagonal planar
  2. B
    tetrahedral
  3. C
    octahedral
  4. D
    trigonal bipyramidal
Show answer

Answer: C. Coordination number 6 places the ligands at the six corners of an octahedron, each at 90° to its neighbours. Coordination number 4 gives tetrahedral or square planar complexes.

6. Which pair of hybridisations of the central metal ion both give an octahedral complex?

  1. A
    dsp2 and sp3
  2. B
    sp3d and sp3d2
  3. C
    d2sp3 and sp3d2
  4. D
    dsp2 and d2sp3
Show answer

Answer: C. Six hybrid orbitals made from two d, one s and three p orbitals point to the corners of an octahedron, whether the d orbitals are inner (n−1)d, as in d2sp3, or outer nd, as in sp3d2. dsp2 gives square planar and sp3 tetrahedral complexes, each with four ligands.

7. Chromium ([Ar] 3d5 4s1) is in its highest oxidation state in potassium chromate, K2CrO4. This oxidation state is

  1. A
    +3
  2. B
    +4
  3. C
    +7
  4. D
    +6
Show answer

Answer: D. 2(+1) + x + 4(−2) = 0 gives x = +6, which uses all five 3d electrons and the one 4s electron, the most chromium can lose. +3 is its most stable state, as in Cr2O3.

8. [Ni(en)3]2+, where en is ethylenediamine (H2NCH2CH2NH2), is much more stable than [Ni(NH3)6]2+, although both have six nitrogen donor atoms. This is because

  1. A
    en is a negatively charged ligand, while ammonia is neutral
  2. B
    each en binds by both N atoms, forming a chelate ring
  3. C
    nickel has a higher oxidation state in the en complex
  4. D
    each nitrogen of en carries more lone pairs than ammonia does
Show answer

Answer: B. A bidentate ligand such as en grips the metal at two points, forming a five-membered chelate ring, and both donor atoms must let go before it can leave; so chelate complexes are more stable than similar complexes of monodentate ligands. Both ligands are neutral, and nickel is +2 in each complex.

9. Which of these 3d metals has the lowest binding energy (weakest metallic bonding)?

  1. A
    chromium
  2. B
    zinc
  3. C
    vanadium
  4. D
    iron
Show answer

Answer: B. Zinc is [Ar] 3d10 4s2: every d electron is paired, so only the two 4s electrons join the metallic bonding, and zinc melts at only about 420 °C. Vanadium and chromium, with the most unpaired d electrons, lie near the maximum.

10. A ground-state atom of a 3d-series element has a filled 4s subshell and four unpaired electrons. What is its atomic number?

  1. A
    24
  2. B
    22
  3. C
    28
  4. D
    26
Show answer

Answer: D. With 4s2, four unpaired d electrons means 3d4 or 3d6. But 3d4 4s2 is not a ground state (chromium is 3d5 4s1), so the atom is [Ar] 3d6 4s2, iron, with Z = 18 + 6 + 2 = 26.

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How many Chemistry · Transition elements MCQs are there?

37, each with the answer and a short explanation, across 2 topics: Properties of transition elements, Complexes. Every chapter test draws ten of them, so you can take it many times.

Is the MDCAT Chemistry chapter 12 test free?

Yes. The test, the answers and the explanations are free and need no sign-up. Sign in only if you want your scores kept across devices.

How is the chapter test marked?

The moment you press Finish: your score, the right answer and an explanation for every question, and the ones you got wrong saved in My mistakes to retry.

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