In the photosynthesis reaction, the general equation is:
\[ 6 , \text{CO}_2 + 6 , \text{H}_2\text{O} \rightarrow , \text{C}6\text{H}{12}\text{O}_6 + 6 , \text{O}_2 \]
This shows that 6 carbon atoms from carbon dioxide (CO₂) are combined to produce one molecule of glucose (C₆H₁₂O₆). Therefore, the correct response is:
6