Identify Bronsted acids in the reaction :H2CO3+HPO2−4⇌H2PO−4+HCO−3
H2CO3 and H2PO−4
The conjugate acid base pairs are
Pair 1: H2CO3; HCO−3, pair 2: HPO2−4; H2PO−4
The acid in these pairs would be the one that has one proton more than the other species.