The correct order of bond angles (smallest first) in ${\mathrm{H}}_2\mathrm{S}, {\mathrm{NH}}_3 , {\mathrm{BF}}_3$ and ${\mathrm{SiH}}_4$ is

Bond angle is ${\mathrm{H}}_2\mathrm{S}$ is near to 90°. Bond angle in ${\mathrm{NH}}_3$ is less than than 109°28' (a perfect tetrahedral angle) due to the electronic repulsion between lone pair and bonded pair. Bond angle in ${\mathrm{SiH}}_{4 }$is 109°28'. Bond angle in ${\mathrm{BF}}_3$ is 120°.