Answer:
The strength of the forces holding the particles of a substance together determines its physical state at a given temperature. The stronger the forces the more energy required to overcome them and hence the particles remain in a fixed position and the substance is solid, while weaker forces may allow the particles to move freely making the substance a gas.
Step-by-step explanation:
In the case of carbon dioxide (CO2), the particles are held together by weak van der Waals forces. These forces are not strong enough to keep the particles in a fixed position, so they are able to move freely and take on the properties of a gas at room temperature.
In the case of water (H2O), the particles are held together by hydrogen bonds. These bonds are stronger than the van der Waals forces in CO2, so the particles are not able to move as freely. As a result, water takes on the properties of a liquid at room temperature.
Salt (NaCl) is made up of positively charged sodium ions (Na+) and negatively charged chloride ions (Cl-). These ions are held together by strong ionic bonds, which keep the particles in a fixed position. As a result, salt takes on the properties of a solid at room temperature.