Which of these is a chemical property of a substance?

density

color

boiling point

flammability

Answer is: flammability.

A chemical property is any of a substance properties that is obvious after chemical reaction.

For example, alcohol is flammable and water is not.

Density, color and boiling point are physical property. Physical property can be observed and measured without any changes in molecular composition. The same substance is present before and after the change.

vanderwaal's forces of attraction are the electrostatic intermolecular forces that exist in a molecule due to the temporary or permanent dipoles that are developed in a molecule. in , the major intermolecular forces are dipole-dipole interactions as the molecule is polar (bent structure). so the vanderwaal's forces of interaction in between molecules are the permanent dipole-dipole interactions that develop due to the dipole that exists in between the polar h - s bond. the positively charged hydrogen atom is attracted towards the negative end of the dipole that is sulfur of the adjacent molecule. therefore, these forces of attraction are relatively stronger than that of london dispersion forces that exist in non polar molecules.