Read the following paragraph and answer the question. Give ONLY the answer, no other words or explanation.

For example:

Answer: <most likely answer, as short as possible>.

Paragraph: 
Mole fractions describe the fraction or percentage of a mixture that is made up of a particular substance.


Question: What describe the fraction or percentage of a mixture that is made up of a particular substance.
mole fractions
Mole fractions describe it.