Explain the differences between mixtures and pure substances

Pure substances cannot be separated into any other kinds of matter, while a mixture is a combination of two or more pure substances.  A pure substance has constant physical and chemical properties, while mixtures have varying physical and chemical properties (i.e., boiling point and melting point).

1.solid

2.carbon dioxide

3.helium

i would say b

explanation:

but i think i would need more information than that