Which of the following statements is not valid for oxoacids of phosphorus?
(a) Orthophosphoric acid s used in the manufacture of triple superphosphate
(b) Hypophosphorus acid is a diprotic acid
(c) All oxoacids contain tetrahedral four coordinated phosphorus
(d) All oxoacids contain at least one P=O unit and one P-OH group
Hypophosphorus acid, H3PO2, has the following structure.
As it contains only one replaceable H-atom (that is attached with O, not with P directly) so it is a monoprotic acid. All other given statements are true.