The group having triangular planar structure is

The group having triangular planar structures is ${\mathrm{CO}}_3^{2-}{\mathrm{NO}}_3^{-},{\mathrm{SO}}_3$
In ${\mathrm{CO}}_3^{2-}$ ion, C atom is ${\mathrm{sp}}^2$ hybridized. This results in triangular planar structure.
$\mathrm{In} {\mathrm{NO}}_3^{-}$ion, N atom is ${\mathrm{sp}}^2$ hybridized. This results in triangular planar structure.
In ${\mathrm{SO}}_3$, S atom is ${\mathrm{sp}}^2$ hybridised. This results in triangular planar structure. 

In all above molecules/ions, the central atom has 3 bonding domains and bond angle of $120°$.
Note:
${\mathrm{NCl}}_3,{\mathrm{NF}}_3$ and ${\mathrm{NH}}_3$ are pyramidal.
${\mathrm{BCl}}_3$ and ${\mathrm{BF}}_3$ have triangular planar structure.

Hence, the correct option is (B)