Which reaction forms a product with a trigonal planar geometry?

Solution:

In all the given reaction it is observed that the ${\mathrm{so}}_3$ has the structure of trigonal planner and all the other molecule has the other structure.

(a)${\mathrm{N}}_2+3{\mathrm{H}}_2\to 2{\mathrm{NH}}_3$ (Pyramidal)

(b) $2\mathrm{CO}+{\mathrm{O}}_2\to 2{\mathrm{CO}}_2$ (Linear)

(c) ${\mathrm{PCl}}_3+{\mathrm{Cl}}_2\to {\mathrm{PCl}}_5$ (TBP)

(d) $2{\mathrm{SO}}_2+{\mathrm{O}}_2\to 2{\mathrm{SO}}_3$ (Trigonal planar)

Sulfur trioxide is known to be a sulfuric acid anhydride. The trigonal planar structure of ${\mathrm{SO}}_3$has a bond angle of ${120}^0$. The triangular planar molecule ${\mathrm{SO}}_3$ in the gas phase requires ${\mathrm{sp}}^2$ hybridization of the S atom.