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Kossel-Lewis approach; ionic and covalent bonds: NEET MCQs with answers

90 questions on this topic of Chemical Bonding and Molecular Structure (NEET 2027 syllabus). Here are 12; tap one to see its answer and explanation.

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easy

1. Which of the following compounds contains both ionic and coordinate covalent bonds in its solid state?

  1. MgCl₂
  2. CH₄
  3. NH₄Cl
  4. NaCl
Show answer and explanation

Answer: (C) NH₄Cl

Ammonium chloride (NH₄Cl) contains ionic bonds between NH₄⁺ and Cl⁻ ions. Within the ammonium cation (NH₄⁺), three N-H bonds are normal covalent bonds and one N-H bond is formed via a coordinate covalent bond where the lone pair of ammonia is donated to an H⁺ ion.

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2. For the nitrite ion (NO₂⁻), what are the formal charges on the nitrogen atom and the two oxygen atoms (designated as double-bonded O and single-bonded O, respectively) in its predominant Lewis structure?

  1. N: 0, double-bonded O: -1, single-bonded O: 0
  2. N: +1, double-bonded O: -1, single-bonded O: -1
  3. N: -1, double-bonded O: 0, single-bonded O: 0
  4. N: 0, double-bonded O: 0, single-bonded O: -1
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Answer: (D) N: 0, double-bonded O: 0, single-bonded O: -1

Nitrogen has 1 lone pair, 1 double bond, and 1 single bond: FC(N) = 5 - 2 - 6/2 = 0. The double-bonded oxygen has 2 lone pairs: FC = 6 - 4 - 4/2 = 0. The single-bonded oxygen has 3 lone pairs: FC = 6 - 6 - 2/2 = -1.

hard

3. Consider the Lewis structure of the nitronium ion, [NO₂]⁺, where nitrogen is the central atom doubly bonded to both oxygen atoms (O=N=O)⁺. What are the formal charges on the central nitrogen atom and each oxygen atom, respectively?

  1. +1 and 0
  2. +1 and -1
  3. 0 and +1
  4. +2 and -1
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Answer: (A) +1 and 0

In [O=N=O]⁺, the central nitrogen has 4 bonding pairs (8 bonding electrons) and 0 lone pairs. Formal charge of N = 5 - 0 - (1/2 × 8) = +1. Each oxygen atom has 2 lone pairs (4 non-bonding electrons) and a double bond (4 bonding electrons). Formal charge of each O = 6 - 4 - (1/2 × 4) = 0.

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4. In the Lewis representation of the nitrite ion, [O=N-O]⁻, what are the formal charges on the double-bonded oxygen, central nitrogen, and single-bonded oxygen atom, respectively?

  1. 0, +1, -2
  2. -1, +1, -1
  3. 0, 0, -1
  4. +1, 0, -2
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Answer: (C) 0, 0, -1

For the double-bonded oxygen: FC = 6 - 4 - (1/2)(4) = 0. For nitrogen: FC = 5 - 2 - (1/2)(6) = 0. For the single-bonded oxygen: FC = 6 - 6 - (1/2)(2) = -1. The respective formal charges are 0, 0, and -1.

easy

5. In which of the following pairs of species does the central atom obey the octet rule completely without being electron-deficient or hypervalent?

  1. BeCl₂ and BCl₃
  2. SF₄ and ClF₃
  3. CCl₄ and NF₃
  4. PCl₅ and AlCl₃
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Answer: (C) CCl₄ and NF₃

In both CCl₄ and NF₃, the central atoms (carbon and nitrogen) share electrons to complete an octet of 8 valence electrons. In BeCl₂ and BCl₃, the central atoms are electron deficient (4 and 6 electrons). In SF₄, ClF₃, and PCl₅, the central atoms have expanded octets (10 electrons).

hard

6. Which of the following orders correctly represents the increasing covalent character of the given alkaline earth metal chlorides according to Fajan's rules?

  1. BaCl₂ < CaCl₂ < MgCl₂ < BeCl₂
  2. BeCl₂ < MgCl₂ < CaCl₂ < BaCl₂
  3. MgCl₂ < BeCl₂ < CaCl₂ < BaCl₂
  4. BaCl₂ < MgCl₂ < CaCl₂ < BeCl₂
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Answer: (A) BaCl₂ < CaCl₂ < MgCl₂ < BeCl₂

According to Fajan's rules, smaller cation size leads to higher polarizing power and greater covalent character. The ionic radii of alkaline earth metal cations follow the trend Be²⁺ < Mg²⁺ < Ca²⁺ < Ba²⁺. Therefore, the polarizing power and covalent character decrease in the order BeCl₂ > MgCl₂ > CaCl₂ > BaCl₂, meaning the increasing order of covalent character is BaCl₂ < CaCl₂ < MgCl₂ < BeCl₂.

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7. Given below are two statements: Statement I: The octet rule accounts for the shape and geometry of polyatomic molecules. Statement II: The octet rule does not explain the difference in relative stabilities of molecules possessing complete octets. In 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
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Answer: (C) Statement I is incorrect but Statement II is correct

Statement I is incorrect because a major limitation of the octet rule is that it cannot predict or explain the shape and geometry of molecules. Statement II is correct because the octet rule is completely silent about the relative stabilities and energies of molecules, even when all constituent atoms satisfy the octet rule.

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8. Which of the following pairs of ions possesses pseudo-noble gas electronic configurations (18 electrons in the outermost shell, ns² np⁶ nd¹⁰)?

  1. Na⁺ and Mg²⁺
  2. Cu⁺ and Zn²⁺
  3. K⁺ and Ca²⁺
  4. Fe²⁺ and Co³⁺
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Answer: (B) Cu⁺ and Zn²⁺

Cu⁺ (atomic number 29 - 1 = 28 electrons) has the configuration [Ar] 3s² 3p⁶ 3d¹⁰. Zn²⁺ (30 - 2 = 28 electrons) also has [Ar] 3s² 3p⁶ 3d¹⁰. These have 18 electrons in the outer third shell, known as a pseudo-noble gas configuration.

easy

9. Which of the following compounds contains an atom that violates the octet rule by possessing fewer than eight electrons in its valence shell?

  1. SiH₄
  2. BeCl₂
  3. NF₃
  4. H₂O
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Answer: (B) BeCl₂

In gaseous BeCl₂, beryllium has 2 valence electrons and forms two single covalent bonds with chlorine atoms, sharing a total of 4 electrons around itself. This represents an electron-deficient central atom with an incomplete octet.

easy

10. Which of the following compounds exhibits an expanded octet (hypervalent state) around its central atom?

  1. CCl₄
  2. SF₆
  3. NH₃
  4. BeCl₂
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Answer: (B) SF₆

In SF₆, the sulfur atom is surrounded by 6 shared electron pairs, giving a total of 12 valence electrons. This exceeds the conventional octet, making it an expanded octet.

easy

11. The nitrogen molecule (N₂) contains a:

  1. Double bond
  2. Ionic bond
  3. Triple bond
  4. Single bond
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Answer: (C) Triple bond

Each nitrogen shares three electrons with the other, forming a triple covalent bond, which gives N₂ its high bond enthalpy.

NCERT Class 11

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12. What is the total number of lone pairs of electrons in the Lewis dot structure of the cyanogen molecule (N≡C-C≡N)?

  1. 6
  2. 4
  3. 2
  4. 0
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Answer: (C) 2

In (CN)₂, each nitrogen atom forms a triple bond with a carbon atom, leaving one lone pair on each nitrogen atom. Carbon has no lone pairs as each carbon forms 4 bonds (one C-C single bond and one C≡N triple bond). Hence, the total number of lone pairs is 1 + 1 = 2.

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