Which statement defines a pure substance?

Which statement defines a pure substance?

• A. A material made of only one type of particle, either an element or a compound.
• B. A mixture of different substances.
• C. A colloid.
• D. A solution of solute and solvent.

Answer: (A)

Pure substances have a definite, uniform composition—every sample contains only one type of particle. That means an element is made of a single kind of atom, while a compound is made of molecules with a fixed ratio of elements. Because the composition is fixed and uniform, pure substances have consistent properties no matter the sample size or source. The statement describing a material made of only one type of particle, either an element or a compound, captures this idea perfectly. A mixture, on the other hand, contains two or more kinds of particles and can vary in composition, so it’s not a pure substance. A colloid is a type of mixture with particles dispersed throughout a medium, not a single pure substance. A solution is a homogeneous mixture of solute and solvent, which also contains more than one chemical species, so it is not a pure substance.

Pure substances have a definite, uniform composition—every sample contains only one type of particle. That means an element is made of a single kind of atom, while a compound is made of molecules with a fixed ratio of elements. Because the composition is fixed and uniform, pure substances have consistent properties no matter the sample size or source. The statement describing a material made of only one type of particle, either an element or a compound, captures this idea perfectly.

A mixture, on the other hand, contains two or more kinds of particles and can vary in composition, so it’s not a pure substance. A colloid is a type of mixture with particles dispersed throughout a medium, not a single pure substance. A solution is a homogeneous mixture of solute and solvent, which also contains more than one chemical species, so it is not a pure substance.