Which one of the following compounds has ${\mathrm{sp}}^2$-hybridization

Hybridization= sigma bond + lone bond.

${\mathrm{SO}}_2$ has 2 sigma bond and 1 lone pair so its hybridization is  ${\mathrm{sp}}^2$.

Sulphur dioxide contains ${\mathrm{sp}}^2$ hybridised, V-shaped sulphur molecules. 

${\mathrm{CO}}_2$ has sp hybridization. 

${\mathrm{N}}_2\mathrm{O}$ has ${\mathrm{sp}}^3$ hybridisation.

$\mathrm{CO}$ has sp hybridisation.