In sp2 hybridisation how to understand the geometry whether which is trigonal planar and which is bent shaped??

see the number of lone pair

You will get your answer when you draw the structure......if there is sp 2 hybridisation there are two possibilities of structures .......you have to write the electronic configuration......if there are no lone pair electrons there will be a regular trigonal structure and if there is one or more lone pair electrons then due to their repulsion the bond angle will increase which distorts the shape of the molecule making its structure bent.........NOTE-the lone pais which are mentioned above are one which are on central atom. ......Eg. take BF3 there is a lone pair left after attaching the F atoms....there is a repulsion between the electron clouds of F atoms and this lone pair which tends to bend the bond of B and F atoms..............