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First-row transition elements: configuration, occurrence and properties: NEET MCQs with answers

88 questions on this topic of d- and f-Block Elements (NEET 2027 syllabus). Here are 12; tap one to see its answer and explanation.

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easy

1. Which of the following gaseous tripositive ions of the 3d-series has the electronic configuration [Ar] 3d²?

  1. Cr³⁺
  2. Ti³⁺
  3. V³⁺
  4. Mn³⁺
Show answer and explanation

Answer: (C) V³⁺

Vanadium has atomic number Z = 23 with ground-state configuration [Ar] 3d³ 4s². On losing three electrons (two from 4s and one from 3d), V³⁺ attains the configuration [Ar] 3d². Ti³⁺ is 3d¹, Cr³⁺ is 3d³, and Mn³⁺ is 3d⁴.

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2. Given below are two statements: Statement I: The melting points of transition metals rise to a maximum near d⁵ configuration and then fall as the atomic number increases. Statement II: Manganese has an anomalously lower melting point compared to its neighbouring elements chromium and iron. In the light of the above statements, choose the most appropriate answer from the options given below:

  1. Both Statement I and Statement II are correct
  2. Statement I is correct but Statement II is incorrect
  3. Statement I is incorrect but Statement II is correct
  4. Both Statement I and Statement II are incorrect
Show answer and explanation

Answer: (A) Both Statement I and Statement II are correct

The melting points of 3d metals increase up to d⁵ configuration due to stronger interatomic metallic bonding involving unpaired d-electrons and then decrease. Manganese has an anomalously low melting point because its half-filled 3d⁵ shell is relatively stable, resulting in weaker metallic bonding. Thus, both statements are correct.

hard

3. Among the first-row transition elements (Sc to Zn), the element having the highest enthalpy of atomisation is:

  1. Titanium
  2. Chromium
  3. Vanadium
  4. Copper
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Answer: (C) Vanadium

Vanadium has the highest enthalpy of atomisation (515 kJ/mol) in the 3d series. Although Cr has more unpaired electrons, vanadium exhibits stronger metallic bonding due to optimal balance of effective nuclear charge and participation of both 3d and 4s electrons without excessive d-d pairing or diffuse expansion.

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4. Consider the following statements regarding the physical properties of the first-row transition metals: (a) All 3d transition metals are typical hard metals with high tensile strength except zinc. (b) The density of transition metals increases from Sc to Cu because of a decrease in atomic radius combined with an increase in atomic mass. (c) The enthalpy of atomisation of Zn is the highest in the 3d series because of its completely filled 3d¹⁰ configuration. Which of the statements given above are correct?

  1. (a) and (b) only
  2. (b) and (c) only
  3. (a) and (c) only
  4. (a), (b) and (c)
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Answer: (A) (a) and (b) only

Statements (a) and (b) are correct. Zn is soft with a low melting point and low tensile strength due to the lack of unpaired d-electrons participating in metallic bonding. Enthalpy of atomisation of Zn is the lowest (126 kJ/mol) in the 3d series, not the highest, precisely because its d-electrons do not participate in metallic bonding. Thus (c) is incorrect.

easy

5. Which of the following ions is expected to be diamagnetic and colourless in aqueous solution?

  1. Sc³⁺
  2. V³⁺
  3. Ti³⁺
  4. Mn²⁺
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Answer: (A) Sc³⁺

Sc³⁺ has an argon core configuration [Ar] 3d⁰. Since it has no d electrons, d-d transitions cannot take place, making it colourless, and having no unpaired electrons makes it diamagnetic.

hard

6. Why is Cr²⁺ a strong reducing agent while Mn³⁺ is a strong oxidising agent, even though both have the 3d⁴ configuration?

  1. Cr³⁺ has a d⁵ configuration, whereas Mn²⁺ has a d³ configuration
  2. Cr²⁺ has a completely filled 4s orbital, while Mn³⁺ has an empty 4s orbital
  3. Cr²⁺ changes to d³ which has a stable half-filled t₂g level in aqueous solution, while Mn³⁺ changes to d⁵ which has a half-filled d-subshell
  4. Hydration enthalpy of Cr²⁺ is exceptionally higher than that of Mn³⁺
Show answer and explanation

Answer: (C) Cr²⁺ changes to d³ which has a stable half-filled t₂g level in aqueous solution, while Mn³⁺ changes to d⁵ which has a half-filled d-subshell

Cr²⁺ acts as a reducing agent because losing one electron gives Cr³⁺ with a 3d³ configuration, which provides extra stability due to a half-filled t₂g³ level in an octahedral aqueous environment. Conversely, Mn³⁺ acts as an oxidising agent because gaining one electron gives Mn²⁺ with a stable half-filled 3d⁵ configuration.

hard

7. Given below are two statements: Statement I: The ionic radius of M²⁺ decreases continuously from Ti²⁺ to Zn²⁺ without any exception. Statement II: The regular decrease in metallic radii of transition elements across a period is disrupted towards the end of the series due to electron-electron repulsions among the 3d electrons. In the light of the above statements, choose the most appropriate answer:

  1. Both Statement I and Statement II are correct
  2. Statement I is correct but Statement II is incorrect
  3. Statement I is incorrect but Statement II is correct
  4. Both Statement I and Statement II are incorrect
Show answer and explanation

Answer: (C) Statement I is incorrect but Statement II is correct

Statement I is incorrect because the curve of ionic radii for M²⁺ ions shows a general decreasing trend but is not perfectly monotonic across the entire series due to crystal field stabilization effects. Statement II is correct because as d-orbitals become fully occupied towards the end of the series (Cu, Zn), increased interelectronic repulsions lead to a slight expansion of atomic/metallic radius.

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8. Match List-I with List-II and select the correct option: List-I (3d Species) (A) Ti⁴⁺ (B) Ni²⁺ (C) Fe³⁺ (D) Co²⁺ List-II (Unpaired electrons) (I) 5 (II) 3 (III) 2 (IV) 0

  1. (A)-(IV), (B)-(III), (C)-(II), (D)-(I)
  2. (A)-(IV), (B)-(I), (C)-(III), (D)-(II)
  3. (A)-(III), (B)-(IV), (C)-(I), (D)-(II)
  4. (A)-(IV), (B)-(III), (C)-(I), (D)-(II)
Show answer and explanation

Answer: (D) (A)-(IV), (B)-(III), (C)-(I), (D)-(II)

Ti⁴⁺ has [Ar] 3d⁰ (0 unpaired electrons); Ni²⁺ has [Ar] 3d⁸ (2 unpaired electrons); Fe³⁺ has [Ar] 3d⁵ (5 unpaired electrons); Co²⁺ has [Ar] 3d⁷ (3 unpaired electrons).

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9. Copper is unique among the 3d-transition series elements because its standard reduction potential E°(M²⁺/M) is positive (+0.34 V). The primary thermodynamic reason for this is:

  1. The high hydration enthalpy of Cu²⁺ cannot compensate for the sum of its enthalpy of atomisation and ionisation enthalpies
  2. Its first ionisation enthalpy is the highest in the series
  3. Its lattice energy in the metallic state is lower than that of all other 3d elements
  4. Its second ionisation enthalpy is exceptionally low due to reaching a d¹⁰ configuration
Show answer and explanation

Answer: (A) The high hydration enthalpy of Cu²⁺ cannot compensate for the sum of its enthalpy of atomisation and ionisation enthalpies

The transformation Cu(s) → Cu²⁺(aq) requires energy for sublimation (atomisation) and ionisation (IE₁ + IE₂). The hydration enthalpy released when Cu²⁺ hydrates is insufficient to counterbalance this required input, making E°(Cu²⁺/Cu) positive.

easy

10. Which of the following transition metal ions has the highest magnetic moment (spin-only) in an aqueous solution?

  1. Fe²⁺
  2. V³⁺
  3. Ti³⁺
  4. Co²⁺
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Answer: (A) Fe²⁺

Electronic configurations: Ti³⁺ has 3d¹ (n = 1), V³⁺ has 3d² (n = 2), Fe²⁺ has 3d⁶ (n = 4 unpaired electrons), and Co²⁺ has 3d⁷ (n = 3 unpaired electrons). Fe²⁺ has the maximum number of unpaired electrons (n = 4), corresponding to μ = √24 ≈ 4.90 BM.

easy

11. Which one of the following 3d-transition series elements exhibits only one positive oxidation state in its common stable compounds?

  1. Titanium
  2. Scandium
  3. Vanadium
  4. Nickel
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Answer: (B) Scandium

Scandium (Z = 21, [Ar] 3d¹ 4s²) readily loses all three valence electrons to attain the stable noble gas configuration of argon. As a result, it exhibits exclusively the +3 oxidation state in its stable compounds.

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12. Given below are two statements: Statement I: The first ionisation enthalpy of Zn is significantly higher than that of Cu. Statement II: Removal of an electron from Zn involves taking an electron from a completely filled 4s orbital of a stable [Ar] 3d¹⁰ 4s² configuration. In the light of the above statements, choose the most appropriate answer:

  1. Both Statement I and Statement II are correct and Statement II is the correct explanation of Statement I.
  2. Both Statement I and Statement II are correct but Statement II is not the correct explanation of Statement I.
  3. Statement I is correct but Statement II is incorrect.
  4. Statement I is incorrect but Statement II is correct.
Show answer and explanation

Answer: (A) Both Statement I and Statement II are correct and Statement II is the correct explanation of Statement I.

Zinc has a completely filled [Ar] 3d¹⁰ 4s² configuration. Its first ionisation enthalpy is exceptionally high because the electron to be removed comes from a stable, fully filled 4s subshell accompanied by a high effective nuclear charge. Thus, both statements are correct and Statement II explains Statement I.

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