3. __ c₈h₁₈ + __o₂ → __co₂ + __h₂o

Explanation:

Step1: Balance carbon atoms

There are 8 carbon atoms in $C_8H_{18}$. So, the coefficient of $CO_2$ should be 8 to balance the carbon atoms. $C_8H_{18}+O_2\rightarrow8CO_2 + H_2O$

Step2: Balance hydrogen atoms

There are 18 hydrogen atoms in $C_8H_{18}$. So, the coefficient of $H_2O$ should be 9 to balance the hydrogen atoms. $C_8H_{18}+O_2\rightarrow8CO_2 + 9H_2O$

Step3: Balance oxygen atoms

On the right - hand side, the total number of oxygen atoms in $8CO_2$ and $9H_2O$ is $8\times2 + 9\times1=16 + 9 = 25$. So, the coefficient of $O_2$ should be $\frac{25}{2}$ to balance the oxygen atoms. But we usually want whole - number coefficients, so we multiply the entire equation by 2. $2C_8H_{18}+25O_2\rightarrow16CO_2 + 18H_2O$

Answer:

2, 25, 16, 18