Chemistry

Problem

Which of the following best defines a pure substance in the context of chemical classification? a)

\text{A uniform material whose composition may vary from one sample to another}

\text{A material composed of atoms of two or more elements combined in variable mass ratios}

\text{A material composed of only one type of particle that cannot be separated into other substances by physical means}

\text{Any solid that has a constant melting point regardless of its composition}