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Physical and chemical trends across periods and down groups: NEET MCQs with answers

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

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easy

1. Given below are two statements: Statement I: Nitrogen exhibits a maximum covalency of 4 in its compounds. Statement II: Nitrogen possesses vacant d-orbitals in its valence shell. In light of the above statements, choose the correct 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
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Answer: (B) Statement I is correct but Statement II is incorrect

Nitrogen has only s and p orbitals in its second valence shell (2s and 2p) and lacks d-orbitals. Consequently, its maximum covalency is restricted to 4, making Statement I correct and Statement II incorrect.

medium

2. The number of lone pairs on the xenon atom in XeO₃ is:

  1. 2
  2. 0
  3. 1
  4. 3
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Answer: (C) 1

Xe has 8 valence electrons; after forming the bonds in XeO₃, 1 lone pair remains.

hard

3. The correct order of increasing thermal stability of Group 14 tetrafluorides is:

  1. CF₄ < SiF₄ < GeF₄ < SnF₄ < PbF₄
  2. PbF₄ < SnF₄ < GeF₄ < SiF₄ < CF₄
  3. SiF₄ < CF₄ < GeF₄ < SnF₄ < PbF₄
  4. PbF₄ < GeF₄ < SnF₄ < CF₄ < SiF₄
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Answer: (B) PbF₄ < SnF₄ < GeF₄ < SiF₄ < CF₄

Due to the inert pair effect, the stability of the +4 oxidation state decreases down Group 14 from carbon to lead. Consequently, the thermal stability of tetrafluorides follows the order PbF₄ < SnF₄ < GeF₄ < SiF₄ < CF₄.

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4. Which of the following statements is INCORRECT regarding the trends in oxidation states of p-block elements?

  1. The maximum oxidation state shown by a p-block element equals the total number of valence electrons (group number minus 10)
  2. The stability of the group oxidation state generally increases down the group
  3. The relative stability of the oxidation state two units less than the group oxidation state increases down Groups 13 to 16
  4. Elements of the second period never show oxidation states exceeding their covalency limit of 4
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Answer: (B) The stability of the group oxidation state generally increases down the group

The stability of the group oxidation state (maximum oxidation state) decreases down the group due to the inert pair effect, while the stability of the state two units lower (group state - 2) increases down the group. Hence, “The stability of the group oxidation state generally incr…” is incorrect.

easy

5. Which of the following orders is correct regarding the acidic strength of the hydrides of Group 16 elements?

  1. H₂O > H₂S > H₂Se > H₂Te
  2. H₂Te > H₂Se > H₂S > H₂O
  3. H₂S > H₂O > H₂Te > H₂Se
  4. H₂Se > H₂Te > H₂S > H₂O
Show answer and explanation

Answer: (B) H₂Te > H₂Se > H₂S > H₂O

Down Group 16, the E-H bond length increases and the bond dissociation enthalpy decreases from H₂O to H₂Te. Consequently, the tendency to release H⁺ ions increases, making H₂Te the most acidic and H₂O the least acidic.

hard

6. Consider the oxoacids of chlorine: HOCl, HClO₂, HClO₃, and HClO₄. The correct order of their relative oxidising ability in aqueous solution is:

  1. HClO₄ > HClO₃ > HClO₂ > HOCl
  2. HClO₂ > HOCl > HClO₄ > HClO₃
  3. HClO₃ > HClO₄ > HClO₂ > HOCl
  4. HOCl > HClO₂ > HClO₃ > HClO₄
Show answer and explanation

Answer: (D) HOCl > HClO₂ > HClO₃ > HClO₄

Although acid strength increases from HOCl to HClO₄, the stability of the conjugate oxoanion also increases dramatically due to resonance delocalisation across multiple oxygen atoms (ClO₄⁻ is very stable). Hence, the tendency to undergo reduction (oxidising power) is highest for HOCl and lowest for HClO₄.

medium

7. The basicity of H₃PO₃ is:

  1. 4
  2. 3
  3. 2
  4. 1
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Answer: (C) 2

Basicity counts the ionisable (O−H) hydrogens. H₃PO₃ has 2 such hydrogens; the P−H hydrogens are not ionisable.

medium

8. Identify the correct sequence regarding the reducing nature of Group 15 hydrides:

  1. NH₃ > PH₃ > AsH₃ > SbH₃ > BiH₃
  2. BiH₃ > NH₃ > SbH₃ > AsH₃ > PH₃
  3. PH₃ > AsH₃ > SbH₃ > BiH₃ > NH₃
  4. BiH₃ > SbH₃ > AsH₃ > PH₃ > NH₃
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Answer: (D) BiH₃ > SbH₃ > AsH₃ > PH₃ > NH₃

The reducing power of Group 15 hydrides depends inversely on the thermal stability of the E-H bond. Down the group, atomic size expands, E-H bond enthalpy decreases, and H-atom release becomes easier; thus BiH₃ is the strongest reducing agent and NH₃ is the weakest.

medium

9. The number of lone pairs on the xenon atom in XeF₂ is:

  1. 1
  2. 0
  3. 2
  4. 3
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Answer: (D) 3

Xe has 8 valence electrons; after forming the bonds in XeF₂, 3 lone pairs remain.

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10. Which of the following Group 16 elements shows the highest tendency to exhibit the +6 oxidation state stably?

  1. Polonium (Po)
  2. Tellurium (Te)
  3. Selenium (Se)
  4. Sulfur (S)
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Answer: (D) Sulfur (S)

The stability of the +6 oxidation state decreases down Group 16, while the stability of the +4 oxidation state increases due to the inert pair effect. Sulfur exhibits stable compounds in the +6 state (e.g., SF₆), whereas Te and Po prefer lower oxidation states.

medium

11. Consider the following Lewis acid strength of boron trihalides: BF₃, BCl₃, BBr₃, and BI₃. The correct order of their relative Lewis acidic strength is:

  1. BF₃ > BCl₃ > BBr₃ > BI₃
  2. BI₃ > BBr₃ > BCl₃ > BF₃
  3. BF₃ > BI₃ > BCl₃ > BBr₃
  4. BCl₃ > BF₃ > BBr₃ > BI₃
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Answer: (B) BI₃ > BBr₃ > BCl₃ > BF₃

The relative Lewis acidity of boron halides is governed by pπ-pπ back-bonding between the filled p-orbital of halogen and the vacant 2p-orbital of boron. This back-bonding is most effective in BF₃ due to favorable 2p-2p orbital overlap and decreases down the group (2p-3p in BCl₃, 2p-4p in BBr₃, 2p-5p in BI₃). Hence, the electron deficiency on boron is least compensated in BI₃, making it the strongest Lewis acid.

easy

12. Which of the following oxides is purely amphoteric in nature?

  1. CO
  2. CO₂
  3. SiO₂
  4. SnO₂
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Answer: (D) SnO₂

CO is neutral; CO₂ and SiO₂ are acidic oxides. SnO₂ (as well as PbO₂) dissolves in both acids and bases to yield salts (e.g., reacting with base to form stannates), exhibiting amphoteric behavior.

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