Since there are no choices, it will be difficult to answer your question.
Let's say these are the choices:
A. The liquid is a pure substance because it is colorless.
B. The liquid is a mixture because its temperature rises.
C. The liquid is a pure substance because it remains liquid when cold.
D. The liquid is a mixture because it has a gas dissolved in a liquid.
your answer is D. The liquid is a mixture because it has a gas dissolved in a liquid.