Which of the following is incorrect about Hypophosphorous acid?

It is also called phosphonic acid

The correct answer is option 1. It is also called phosphonic acid.

Hypophosphorous acid, also known as phosphinic acid, is an oxoacid of phosphorus in which, the oxidation state of phosphorus is +1. It is monobasic in nature, that is, it dissociates to produce one hydrogen ion. It is represented by the formula H₃PO₂.