Answer :

Certainly! To determine which molecules are compounds, we need to understand the definition of a compound. A compound is a molecule that contains at least two different elements.

Let's analyze each molecule:

1. [tex]$NaHCO_3$[/tex]:
- Elements contained: Sodium (Na), Hydrogen (H), Carbon (C), and Oxygen (O).
- Conclusion: This molecule contains four different elements, so it is a compound.

2. [tex]$O_3$[/tex]:
- Elements contained: Only Oxygen (O).
- Conclusion: This molecule contains only one type of element, so it is not a compound.

3. [tex]$Cl_2$[/tex]:
- Elements contained: Only Chlorine (Cl).
- Conclusion: This molecule contains only one type of element, so it is not a compound.

4. [tex]$C_8H_{18}$[/tex]:
- Elements contained: Carbon (C) and Hydrogen (H).
- Conclusion: This molecule contains two different elements, so it is a compound.

Based on the analysis, the two molecules that are compounds are:
- [tex]$NaHCO_3$[/tex]
- [tex]$C_8H_{18}$[/tex]

Therefore, the correct answers are:
- [tex]$NaHCO _3$[/tex]
- [tex]$C_8 H _{18}$[/tex]