What is the n-factor / valency factor of H2CO3 ?
Either a or b
In this case of H2CO3 valency factor changes depending upon the reaction as the number of H+ ions replaced might vary depending on the extent of the reaction.
H2CO3 → H+ + HCO3− (n-factor =1)
H2CO3 → 2H+ +CO32− (n-factor = 2)