NEET 2023 Chemistry Octet Rule MCQ Question

To determine the total number of species that do not have eight electrons around the central atom in their outermost shell, we need to analyze each of the given compounds: NH₃, AlCl₃, BeCl₂, CCl₄, and PCl₅. We will evaluate the electron configuration of the central atom in each molecule and check how many valence electrons surround it.

1. Analysis of Each Species

a) NH₃ (Ammonia)

• Central Atom: Nitrogen (N)
• Valence Electrons: Nitrogen has 5 valence electrons. In NH₃, nitrogen forms three single bonds with hydrogen atoms.
• Total Electrons Around N: 5 (from nitrogen) + 3 (from hydrogen) = 8
• Conclusion: Nitrogen has 8 electrons around it.

b) AlCl₃ (Aluminum Chloride)

• Central Atom: Aluminum (Al)
• Valence Electrons: Aluminum has 3 valence electrons. In AlCl₃, it forms three bonds with chlorine atoms.
• Total Electrons Around Al: 3 (from aluminum) + 6 (from three chlorine atoms, each contributing one electron) = 6
• Conclusion: Aluminum does not have 8 electrons around it.

c) BeCl₂ (Beryllium Chloride)

• Central Atom: Beryllium (Be)
• Valence Electrons: Beryllium has 2 valence electrons. In BeCl₂, it forms two bonds with chlorine atoms.
• Total Electrons Around Be: 2 (from beryllium) + 2 (from two chlorine atoms, each contributing one electron) = 4
• Conclusion: Beryllium does not have 8 electrons around it.

d) CCl₄ (Carbon Tetrachloride)

• Central Atom: Carbon (C)
• Valence Electrons: Carbon has 4 valence electrons. In CCl₄, it forms four single bonds with chlorine atoms.
• Total Electrons Around C: 4 (from carbon) + 4 (from four chlorine atoms, each contributing one electron) = 8
• Conclusion: Carbon has 8 electrons around it.

e) PCl₅ (Phosphorus Pentachloride)

• Central Atom: Phosphorus (P)
• Valence Electrons: Phosphorus has 5 valence electrons. In PCl₅, it forms five bonds with chlorine atoms.
• Total Electrons Around P: 5 (from phosphorus) + 5 (from five chlorine atoms, each contributing one electron) = 10
• Conclusion: Phosphorus does not have 8 electrons around it.

2. Summary of Findings

• NH₃: 8 electrons (satisfies octet rule)
• AlCl₃: 6 electrons (does not satisfy octet rule)
• BeCl₂: 4 electrons (does not satisfy octet rule)
• CCl₄: 8 electrons (satisfies octet rule)
• PCl₅: 10 electrons (does not satisfy octet rule)

3. Total Count of Species Not Satisfying the Octet Rule

From our analysis:

• Species not having 8 electrons: AlCl₃, BeCl₂, PCl₅
• Total Count: 3 species

4. Conclusion

Thus, the total number of species that do not have eight electrons around the central atom is 3. Therefore, the correct answer is D) 3.

Additional Clarification

• The octet rule states that atoms tend to form compounds in such a way that each atom has eight electrons in its valence shell, leading to more stable electronic configurations.
• In cases like BeCl₂ and AlCl₃, these compounds exhibit electron deficiency and do not complete the octet.

In conclusion, the final answer to the question is indeed D) 3, as three of the provided species do not have eight electrons around their central atom.