Correct Answer – 4
Like ammonia, trihalides have pyramidal shapes, i.e. the central atom is `sp^(3)` hybridized. There of the four `sp^(3)`-orbitals from `sigma`-bonds with halgon atoms while the fourth `sp^(3)`-orbital contains the lone pair of electrons.
The bond angles of the trihalides of an element decrease as the electronegativity of the halogen increasese, i.e. `underset((96.3^(@)))(PF_(3)) lt underset((100.4^(@)))(PCl_(3)) lt underset((101^(@)))(PBr_(3)) lt underset((102^(@)))(PI_(3))`
As the electronegativity of halgen increases , the bond pairs move away from the central `P` atom. As a result lone pairs -bond hair replusions increase while bond pair-bond pair repulsions decreases .Consequently the bond angles increase.