so₂ + h₂ → h₂s + h₂o

Explanation:

Step1: Balance sulfur atoms

The number of sulfur atoms on the left - hand side is 1 in $SO_2$ and on the right - hand side is 1 in $H_2S$. So, for sulfur, the coefficient of $SO_2$ and $H_2S$ can be adjusted to balance sulfur. Let the coefficient of $SO_2$ be 1 and the coefficient of $H_2S$ be 1 for now. $SO_2 + H_2\rightarrow H_2S + H_2O$

Step2: Balance oxygen atoms

There are 2 oxygen atoms in $SO_2$. In $H_2O$, to balance the oxygen atoms, since there are 2 oxygen atoms in $SO_2$, the coefficient of $H_2O$ should be 2. $SO_2 + H_2\rightarrow H_2S+2H_2O$

Step3: Balance hydrogen atoms

On the right - hand side, in $H_2S$ and $2H_2O$, the total number of hydrogen atoms is $2 + 2\times2=6$. So, the coefficient of $H_2$ on the left - hand side should be 3. $SO_2 + 3H_2=H_2S + 2H_2O$

Answer:

$1SO_2+3H_2 = 1H_2S+2H_2O$