Question

18CO₂ + 18H₂O ----energy-----> 3C₆H₁₂O₆ + _?_O₂

Answer 1

Answer:

18  

Explanation:

8CO₂ + 18H₂O + energy ⟶ 3C₆H₁₂O₆ + O₂

C is balanced .

We have 54 O on the left-hand side, but only 20 O on the right-hand side.  

We need 34 more O atoms on the right, for a total of 36. Put an 18 in front of O₂.

18CO₂ + 18H₂O + energy ⟶ 3C₆H₁₂O₆ + 18O₂

Check:

$\begin{array}{ccc}\textbf{Atom} & \textbf{On the left} & \textbf{On the right}\\\text{C} &18 &18\\\text{H} & 36 & 36\\\text{O} & 54 &54\\\end{array}$

It checks.