A chemical analysis is needed.
Any chemical may be pure or impure.
pure
Salt can be purchased in any form: solid or solution, pure or impure, fine, coarse, etc.
Pure
impure
Pure water does not contain colour but impure water contains Other compounds.
Impure naphthalene will typically melt faster than pure naphthalene. The impurities present in impure naphthalene lower its melting point, making it easier for the solid to convert into a liquid state at a lower temperature.
Generally an impure material is cheaper than a pure material; the word advantage is not so adequate here - can use pure or impure, this depends on the specific applications.
The suitable prefix for pure is pure it won't make sense of you put another set of words in front of pure it just would not make
impure
For a simple experiment to distinguish between pure and impure naphthalene, you can try sublimation. Place a small amount of naphthalene in a test tube and heat it gently. If the naphthalene sublimes (converts from solid to gas without melting), leaving no residue, it is likely pure. However, if there is residue left behind, it suggests the naphthalene is impure.
mixture