The covalency of carbon in the $\mathrm{CO}$ molecule is three because

Select the correct statement(s).

($\mathrm{I}$) Polarizability of ${\mathrm{S}}^{2-}$ is lower than ${\mathrm{Se}}^{2-}$
($\mathrm{II}$) Polarizability of ${\mathrm{S}}^{2-}$ is higher than ${\mathrm{Cl}}^{-}$
($\mathrm{III}$) Polarizability of ${\mathrm{S}}^{2-}$ is lower than ${\mathrm{P}}^{3-}$
($\mathrm{IV}$) Polarizability of ${\mathrm{O}}^{2-}$ is higher than ${\mathrm{S}}^{2-}$

1. ${\mathrm{CH}}_3{\mathrm{CH}}_2{\mathrm{CH}}_2\mathrm{CHO}$

2. ${\mathrm{CH}}_3\mathrm{CH}=\mathrm{CHCHO}$

3. ${\mathrm{CH}}_3{\mathrm{CH}}_2\mathrm{CH}={\mathrm{CH}}_2$

The geometry around how many carbon atoms is tetrahedral in the given structure?