Question

Assertion :In $S{O}_2$, the bond angle is ${119}^{\circ }$ whereas in $S{O}_3$, the bond angle is ${120}^{\circ }$. Reason: $S$ atom in both $S{O}_2$ and $S{O}_3$ is $s{p}^2$-hybridized.

• A. If both assertion and reason are CORRECT and reason is the CORRECT explanation of the assertion.
• B. If both assertion and reason are CORRECT, but reason is NOT THE CORRECT explanation of the assertion.
• C. If assertion is CORRECT, but reason is INCORRECT.
• D. If assertion is INCORRECT, but reason is CORRECT.

Answer 1

The correct option is B If both assertion and reason are CORRECT, but reason is NOT THE CORRECT explanation of the assertion.

There are 3 bonding sets of electrons and one non-bonding pair on the sulphur. So the shape is based on a tetrahedral structure - but the extra repulsion of the non-bonding pair will decrease the O-S-O angles by a few degrees from the 'perfect' tetrahedral angle.
The bonding in $S{O}_3$ can be described as a combination of 3 resonance forms of 1 double and 2 single bonds.
The $S{O}_2$ molecule has a dipole moment, The starting point of 109.5 degrees is only applicable for 4 electron regions round the central atom. In $S{O}_2$, we have 2 double bonds and one lone pair ; 3 electron regions so the default angle is 120 degrees. The extra repulsion of the lp vs double bonds accounts for reduction to 119.
S atom in both $S{O}_2$ and $S{O}_3$ is sp2-hybridized. But it is related to dipole moment and assertion is the explanation from bent angle so here reason is unable to give explanation of assertion.