AB₃ type polar molecules form when: 

• A

  $\text{Lone pair on }\mathrm{A}=\text{zero, only }3 \mathrm{\sigma }\text{-bonds in }{\mathrm{AB}}_3$

• B

  $\text{Lone pair on }\mathrm{A}=\text{one, only }3\mathrm{\sigma }\text{-bonds in }{\mathrm{AB}}_3$

• C

  $\text{Lone pair on }\mathrm{A}=\text{two, only}3\mathrm{\sigma }\text{-bonds in }{\mathrm{AB}}_3$

• D

  $\text{Lone pair on }\mathrm{A}=\text{one,}3\mathrm{\sigma }\text{- and }3\mathrm{\pi }\text{-bonds in }{\mathrm{AB}}_3$