Write the chemical formula of Potassium nitrate in a step-by-step manner.

Step 1 — Write each symbol with its valency

$\text{K}^{1+} \phantom{\nearrow} \text{NO}_3^{1-}$

Step 2 — Interchange the valencies

$\overset{\phantom{2}{1}}{\text{K}} \space {\searrow}\mathllap{\swarrow} \space \overset{1}{\text{NO}$3} \Rightarrow \underset{\phantom{1}{1}}{\text{K}} \space {\searrow}\mathllap{\swarrow} \space \underset{1}{\text{NO}3} \\[0.5em]

Step 3 — Write the interchanged number & hence the formula

Therefore, we get

Formula of Potassium nitrate : $\bold{KNO}_\bold{3}$