Which statement best describes chemical properties of matter? chemical properties, such as density, must be observed when a substance is in its natural state at room temperature and normal atmospheric pressure. chemical properties, such as reactivity, must be observed when a substance is in its natural state at room temperature and normal atmospheric pressure. chemical properties, such as combustibility, are generally observed as the identity of a substance changes and one or more new substances form. chemical properties, such as boiling point, are generally observed as the identity of a substance changes and one or more new substances form.

Chemical change involves formation of new substances. Hence, the correct answer is "Chemical properties, such as combustibility, are generally observed as the identity of a substance changes and one or more new substances form."

The principal thing about a chemical change is that the identity of the substance must change. The identity of the substance must change as bonds between atoms of the substance are broken and rearranged.

Combustibility is a chemical property. It is observed as a substance is transformed into its oxide giving out heat and light in the process.

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hydrocarbons are organic compounds that contain only hydrogens and carbons. they can be saturated (those which contain only carbon-carbon single bonds) or unsaturated (those which contain carbon-carbon double or triple bonds) in nature. hydrocarbons can undergo several reactions like substitution, elimination etc.  

on substituting one or more hydrogen atoms in hydrocarbon it results in the formation of haloalkane. as the halogen atoms are large compared to the carbon and hydrogen atoms, due to which the molecular weight increases and the bond become polar because of presence electronegative halogen atom and results in the increase in boiling point of the haloalkane.

thus, the correct option is (b) that is the boiling point of the new compound increases on substituting a hydrogen atom with a halogen in a hydrocarbon.