Question

which of these elements is not present in $\text{nano}_3$?
nitrogen
sodium
hydrogen
oxygen

Explanation:

First, identify the elements in the chemical formula $\text{NaNO}_3$: $\text{Na}$ is sodium, $\text{N}$ is nitrogen, and $\text{O}$ is oxygen. Hydrogen ($\text{H}$) does not appear in the formula.

Answer:

hydrogen