Which of the following is not tetrahedral in shape?
In NH4+ the central atom is sp3hyberdised. Therefore it has tetrahedral shape.
In SiCl4 also central atom is sp3hyberdised. Therefore it has tetrahedral shape.
In SO42 also central atom is sp3hyberdised. Therefore it has tetrahedral shape,but
SF4 does not have tetrahedral shape because it have sp3d hyberdisation.
Thus it shows trigonal bipyramidal shape. Hence the correct answer is (iii)