Provided association equation associated with the K2 value for the tripodic acid of pyrophosphosphoric acid. Here we're going to say K2 means we're dealing with losing its second H+ ion, meaning that we've already lost the first H+ ion.
If we've already lost the 1st, that means we're starting out now as H3P2O7-, 1. Here it would react with water. Since it's acting as an acid, it would donate an H+ to the water molecule. Doing so would change it into H2P2O72- aqueous and then water.
Accepting an H would become H3O+. This would represent the equation associated with the K2 of this particular triprotic acid.