MCQ Detailed View

The concept of valency refers to the combining capacity of an atom, which is determined by the number of electrons it can gain, lose, or share to complete its outermost shell. A carbon atom has an atomic number of 6, meaning its electronic configuration is 1s² 2s² 2p². This places 4 electrons in its outermost shell (2s² 2p²). Since the outer shell requires 8 electrons for stability, carbon needs 4 more electrons to complete its octet.

Therefore, the valency of carbon is 4, because it can form four covalent bonds by sharing its four valence electrons with other atoms. This tetravalency makes carbon unique and is the reason for the vast diversity of organic compounds.

For example, in methane (CH₄), carbon shares one electron with each of the four hydrogen atoms, completing its octet while giving hydrogen atoms their stable configuration. Carbon can also form double bonds, as in ethene (C₂H₄), or triple bonds, as in ethyne (C₂H₂), while still following its tetravalency.

Examining the options:

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  Valency 1 is incorrect, as carbon cannot satisfy its octet with just one bond.

  
  


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  Valency 2 applies to elements like oxygen, not carbon.

  
  


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  Valency 3 belongs to elements such as nitrogen.

  
  


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  Valency 4 is correct, as carbon consistently forms four bonds.

  
  

Carbon’s tetravalency also allows it to form chains, rings, and branched structures, which is the basis of organic chemistry. This property explains why carbon can form millions of stable compounds, more than any other element in the periodic table.