4. (5 marks) a) White phosphorus is a tetrahedral molecule with the corresponding point group Td. It is an important industrial chemical for the production of many organophosporus molecules. It has been shown possible recently to replace one P with an As to yield AsP3 and As2P2 has also been proposed. Draw the correct structures for these and assign the proper point group. For the latter, be sure to indicate your reasoning. b) Consider the cyclo-triphosphinophosphonium ion the Lewis structure for which is illustrated. Draw the VSEPR structures for the two stereoisomers possible, identify the symmetry elements present and assign the correct point group (consider the methyl groups as spherical substituents)