Why is the stability of a compound considered a chemical property?

Here is the explanation of the given question above. When we say chemical stability, it refers whether the chemical will react with air or water because a substance that is stable will not react. When the compound is unstable, this results in the breakdown and formation of a new substance which results in a chemical change. 

The answer is c) pyrite

3-isopentane; 3-methylbutane, and 1,2-methylpropane do not meet iupac rules, so they are wrong names.the only valid name onthe list is 2-methylbutane, which is the same isopentane.this is its formula:                   ch2                    |ch3 - ch - ch2 - ch3answer: 2-methylbutane