The molecular formula of sodium citrate is Na3C6H5O7. This means that one molecule of sodium citrate contains:

- 3 atoms of sodium (Na)

- 6 atoms of carbon (C)

- 5 atoms of hydrogen (H)

- 7 atoms of oxygen (O)

In total, one molecule of sodium citrate contains 3 + 6 + 5 + 7 = 21 atoms.