To determine the chemical formula of water, we can analyze each of the given options:
1. [tex]$N_2O$[/tex] - This is the chemical formula for nitrous oxide, commonly known as laughing gas.
2. [tex]$H_2O$[/tex] - This is the correct representation of water. It consists of 2 hydrogen atoms and 1 oxygen atom bonded together.
3. [tex]$NH_3$[/tex] - This is the chemical formula for ammonia, which consists of 1 nitrogen atom and 3 hydrogen atoms.
4. [tex]$HO_3$[/tex] - This is not a valid chemical formula for any common compound.
Based on this analysis, the correct answer is [tex]$H_2O$[/tex]. Therefore, the chemical formula of water is encoded by the numerical index:
[tex]\[
H_2O = 2
\][/tex]
So, the answer to the question "What is the chemical formula of water?" is option 2, [tex]$H_2O$[/tex].
