Question

NH3 is pyramidal while BF3 is trigonal planar, though both are tetra atomic molecules

Answer 1

NH3 has 1 lone pair of electon due to which there is lone pair-bond pair repulsion occurs...and push the bond..therefore the shape is pyramidal...while BF3 has no lone pair of electron left and exhibit trigonal planar structure

Answer 2

NH3 is pyramidal bcoz their angle is 107° and BF3 is trigonal planner bcoz their angle is 109°.