Find the number of species having bond angle less than 109°28'.

${\mathrm{NH}}_3,{\mathrm{PH}}_3,{\mathrm{SiH}}_4,{\mathrm{NH}}_4^{+},{\mathrm{PF}}_3,{\mathrm{NH}}_2^{-},{\mathrm{SO}}_3,{\mathrm{NO}}_2^{+},{\mathrm{CCl}}_4$

${\mathrm{H}}_2\mathrm{O},{\mathrm{H}}_2\mathrm{S},{\mathrm{SO}}_4^{2-}$

Trigonal pyramidal is the ${\mathrm{NH}}_3$ molecule's molecular shape. The lone pair of electrons on the nitrogen atom resist the hydrogen atoms, causing the NH3 bond angle to be 107 degrees.
species with bond angles less 109°28'.

${\mathrm{NH}}_3,{\mathrm{PH}}_3,{\mathrm{NH}}_2^{\ominus },{\mathrm{PF}}_3,{\mathrm{H}}_2\mathrm{O},{\mathrm{H}}_2\mathrm{S}$