The total number of stereoisomers of C4H8O3 that evolve CO2 with NaHCO3(aq) is 8. Stereoisomers are compounds that have the same molecular formula and connectivity of atoms but differ in how their atoms are arranged in space. In this case, we are interested in the stereochemistry of the compound and how it affects its reactivity with NaHCO3(aq) to produce CO2.

There are several factors to consider when determining the number of stereoisomers of a compound:

1. Number of chiral centers: Chiral centers are carbon atoms that are bonded to four different groups. They can have two different configurations, known as R and S. The number of stereoisomers can be calculated using the formula 2^n, where n is the number of chiral centers.

2. Symmetry: Compounds with symmetry may have fewer stereoisomers than expected based on the number of chiral centers. This is because some stereoisomers may be identical due to the symmetry of the molecule.

3. Geometric isomerism: Compounds with double bonds can exhibit cis-trans isomerism. This occurs when two different groups are attached to each carbon of the double bond and can be either on the same side (cis) or opposite sides (trans). Each cis-trans isomer can be considered as a separate stereoisomer.

Now let's consider the compound C4H8O3. To determine the number of stereoisomers, we need to identify the chiral centers and the presence of geometric isomerism:

Chiral centers: To identify the chiral centers, we look for carbon atoms bonded to four different groups. In C4H8O3, there are two chiral centers, indicated by the asterisks below:

H H H H
| | | |
H3C*—C—(O)C—(O)C—C*—H
| | | |
H H H H

Stereoisomers with chiral centers: Since there are two chiral centers, we can calculate the number of stereoisomers using the formula 2^n. In this case, 2^2 = 4 stereoisomers.

Geometric isomerism: The compound also contains a double bond between the two central carbon atoms. This means that each of the four stereoisomers can exist in two different geometric isomers, cis and trans. Therefore, we multiply the number of stereoisomers by 2: 4 * 2 = 8 stereoisomers.

Therefore, the total number of stereoisomers of C4H8O3 that evolve CO2 with NaHCO3(aq) is 8.