Each oxy-acid contains at least one X−OH unit (X is non-metal). The H-atom of X−OH unit is ionisable and the number of −OH groups directly attach to non-metal decides the basicity of oxy-acid. Which of the following hypoform of oxy-acid can exhibit tautomerism ?
a. H2N2O2
b. H4P2O6
c. H2S2O6
d. H3PO3