Question

which of the lewis structures in the image is correct? a b c d

Explanation:

• Option A: Phosphorus has 5 valence electrons and each chlorine has 7. In \(PCl_3\), phosphorus forms 3 single bonds with chlorine atoms. Each bond accounts for 2 electrons. After forming 3 bonds, phosphorus has 1 lone - pair (\(5-(3\times1) = 2\) electrons as a lone - pair) and each chlorine has 3 lone - pairs (\(7 - 1=6\) electrons as 3 lone - pairs). This structure follows the octet rule (except for some hypervalent cases, but \(PCl_3\) is a common compound that follows the octet rule for all atoms).
• Option B: In \(SO_2\), sulfur should have a double bond with one oxygen and a single bond with another oxygen (resonance structures exist). The given structure does not account for the correct bonding and electron distribution. Sulfur has 6 valence electrons. If it forms two single bonds with oxygen (each oxygen has 6 valence electrons), the electron count is not correct for a stable \(SO_2\) structure. A more correct Lewis structure has a double bond (\(S = O\)) and a \(S - O\) single bond with a lone - pair on sulfur.
• Option C: Carbon has 4 valence electrons. In the given structure, carbon is bonded to a hydrogen (1 valence electron) and two other hydrogens. But the double - bond with sodium is incorrect. Sodium is a metal and forms ionic bonds, not covalent double - bonds in a simple Lewis structure of a molecular compound.
• Option D: Carbon has 4 valence electrons. In \(CBr_3\), carbon should form 4 covalent bonds (to satisfy the octet rule). Here, carbon only has 3 bonds (with 3 bromine atoms), so it does not follow the octet rule for carbon.

Answer:

A.