The answer to this question would be: zero
The net change is zero because the number of shared electron pairs is not changed. In H2CO3 there are 2 pairs of shared electron in O-H bond, 2 pairs of shared electron in C-OH bond and 2 pairs of shared electron in C-O bond. So the total pairs is 6
In H2O there are 2 pairs of shared electron in O-H bond and in CO2 4 pairs of shared electron in C-O bond. The total pair is still 6
