How many molecules among the following have zero dipole moment: NH₃, BF₃, NF₃, CCI₄?

$\text{ i. }\ddot{\mathrm{N}}{\mathrm{H}}_3\Rightarrow {\mathrm{sp}}^3\text{ hybridised }\Rightarrow \text{ pyramidal }\Rightarrow \mathrm{\mu }\ne 0$

$\text{ ii. }{\mathrm{BF}}_3\Rightarrow {\mathrm{sp}}^2\text{ hybridised }\Rightarrow \text{ planar and symmetrical }$$\Rightarrow \mathrm{\mu }=0.$

$\text{ iii. }{\ddot{\mathrm{NF}}}_3\Rightarrow {\mathrm{sp}}^3\text{ hybridised }\Rightarrow \text{ pyramidal }\Rightarrow \mathrm{\mu }\ne 0\text{. }$

$\text{ iv. }{\mathrm{CCl}}_4\Rightarrow {\mathrm{sp}}^3\text{ hybridised }\Rightarrow \text{ symmetrical }\Rightarrow \mathrm{\mu }=0$

Hence, BF₃ and CCl₄ have zero dipole moment.