Balance each equation. K + O₂ → K₂O; H₂ + Br₂ → HBr; K + H₂O → KOH + H₂; Fe + O₂ → Fe₂O₃

Step 1. (a) $4\text{K} + \text{O}_2 \rightarrow 2\text{K}_2\text{O}$.

Step 2. (b) $\text{H}_2 + \text{Br}_2 \rightarrow 2\text{HBr}$.

Step 3. (c) $2\text{K} + 2\text{H}_2\text{O} \rightarrow 2\text{KOH} + \text{H}_2$: H $4 = 4$, O $2 = 2$.

Step 4. (d) Oxygen: $2$ and $3$ meet at $6$, so $3\text{O}_2$ and $2\text{Fe}_2\text{O}_3$; then $4\text{Fe}$: $4\text{Fe} + 3\text{O}_2 \rightarrow 2\text{Fe}_2\text{O}_3$.