To determine which of the given substances is a molecule but not a compound, we need to start by understanding the definitions of a molecule and a compound.
- Molecule: A molecule is formed when two or more atoms join together chemically.
- Compound: A compound is a type of molecule that contains at least two different elements.
Given this, let's analyze each of the substances:
1. [tex]\(H_2\)[/tex] (Hydrogen Gas):
- [tex]\(H_2\)[/tex] consists of two hydrogen atoms bonded together.
- Since it is composed of only one type of element (hydrogen), it is a molecule but not a compound.
2. NaCl (Sodium Chloride):
- NaCl consists of sodium (Na) and chlorine (Cl) atoms bonded together.
- It includes two different elements, making it a compound.
- Therefore, NaCl is both a molecule and a compound.
3. CO (Carbon Monoxide):
- CO consists of carbon (C) and oxygen (O) atoms bonded together.
- It has two different elements, so it is a compound.
- Thus, CO is both a molecule and a compound.
4. [tex]\(CO_2\)[/tex] (Carbon Dioxide):
- [tex]\(CO_2\)[/tex] consists of one carbon (C) atom and two oxygen (O) atoms.
- Since it contains two different elements, it is considered a compound.
- Therefore, [tex]\(CO_2\)[/tex] is both a molecule and a compound.
After evaluating each substance, we can conclude that:
- The substance that is a molecule but not a compound is [tex]\(H_2\)[/tex].
Therefore, the correct answer is:
[tex]\[ \boxed{H_2} \][/tex]
