a. Phosphorous pentachloride ( PCl5 ) has a trigonal bipyramidal structure. Here, the five bonds are not of equal lengths as the axial bonds are slightly longer than the equatorial bonds. b. PCl5 solid exists as [PCl4]+ and [PCl6]− and they have tetrahedral and octahedral structures respectively. c. On hydrolysis, PCl5 gives H3PO4 which is tribasic. PCl5+4H2O→H3PO4+5HCl d. In H3PO4,P is in its +5 oxidation state. So it is in its highest oxidation state and hence is not a good reducing agent.