Answer;
30 atoms
Step-by-step explanation;
When glucose, C6H12O6, reacts with oxygen it produces carbon dioxide and water. If a molecule of glucose reacts completely with three molecules of oxygen, then 30 atoms would be produced because there are 24 atoms in glucose and 6 atoms in oxygen molecules.
The equation for the reaction would be;
C6H12O6 + 6O2(g) → 6CO2(g) + 6 H2O(l)