Number of moles of a substance can be calculated from mass of the substance and its molar mass as follows:
Here, n is number of moles, m is mass and M is molar mass.
For aspirin: 324 mg
Molecular formula is and molar mass of aspirin is 180.157 g/mol, thus, number of moles will be:
For sodium hydrogen carbonate: 1904 mg
Molecular formula is and molar mass is 84.007 g/mol, thus, number of moles will be:
For citric acid: 1000 mg
Molecular formula is and molar mass is 192.124 g/mol, thus, number of moles will be:
Therefore, number of moles of aspirin, and citric acid in the tablet is 0.0018 mol, 0.0226 mol and 0.0052 mol respectively.