Correct Option
The correct option is (a).
Explanation
Valency is a fundamental chemical property that defines how atoms of an element combine with other atoms. It is determined by the number of electrons present in the outermost shell (valence shell) of an atom and is governed by the tendency of atoms to achieve a stable electronic configuration.
Statement-wise Analysis:
- Statement 1 is Correct: Valency is defined as the combining capacity of an atom of an element. It represents the number of electrons an atom needs to lose, gain, or share to achieve a stable noble gas configuration.
- Statement 2 is Incorrect: Atoms react to achieve a stable configuration, which is usually an octet (8 electrons) in the outermost shell. The duplet (2 electrons) configuration is achieved only by elements where the outermost shell is the K-shell (e.g., Hydrogen, Helium, Lithium, Beryllium). Therefore, atoms do not achieve a duplet in "all cases."
- Statement 3 is Incorrect: If the outermost shell has 8 electrons (as seen in Noble Gases like Neon or Argon), the atom is already stable and has little to no tendency to react. Consequently, its combining capacity is zero. Thus, if the number of valence electrons is 8, the valency is 0, not 8.
Key Takeaway:
Valency is distinct from the number of valence electrons. For elements with 1 to 4 valence electrons, valency equals the number of valence electrons. For elements with 5 to 8 valence electrons, valency is generally calculated as 8 minus the number of valence electrons.