The correct order of bond angles (smallest first) in H2S, NH3, BF3 and SiH4 is-
Let's, try to determine the geometry and structure of each compound.
H2S⇒ep=V+L+A−C2=6+22=4⇒Tetrahedral
NH3⇒ep=V+L+A−C2=5+32=4⇒Tetrahedral
SiH4⇒ep=4+42=4⇒Tetrahedral
BF3⇒ep=3+32=3⇒ Trigonal Planar
H2S⇒
NH3⇒
SiH4⇒
BF3⇒
In trigonal Planar, the bond angle is 120o. The angles for the other compounds correspond to:
NH3⇒ Around 107o
H2S⇒ Around 104.5o
SiH4⇒ Around 109.5o
Therefore, the order will be
H2S< NH3< SiH4< BF3