It is Trigonal bipyramidal because it has 4 bond pair with a lone pair. It has one atom at the centre which is Se and 4 bond pair that are bonded to it that is flourine which form triangonal inform of triangles . If the lone pair is placed at axial position the angle will be 90
degreess Celsius and if it is at equitorial position, the angle will be 120 degrees.
