Write the chemical formula of Sodium bromide in a step-by-step manner.

Step 1 — Write each symbol with its valency

$\text{Na}^{1+} \phantom{\nearrow} \text{Br}^{1-}$

Step 2 — Interchange the valencies

$\overset{\phantom{2}{1}}{\text{Na}} \space {\searrow}\mathllap{\swarrow} \space \overset{1}{\text{Br}} \Rightarrow \underset{\phantom{1}{1}}{\text{Na}} \space {\searrow}\mathllap{\swarrow} \space \underset{1}{\text{Br}} \\[0.5em]$

Step 3 — Write the interchanged number & hence the formula

Therefore, we get

Formula of Sodium bromide : $\bold{NaBr}$