Two basic properties of the gas phase are

The choices can be found elsewhere and as follows:

A.) a definite shape and a definite volume

B.) a definite shape but no definite volume

C.) no definite shape and no definite volume

I believe the correct answer is option C. Two basic properties of the gas phase would be it has no definite shape and no definite volume. It takes the shape and volume of its container. Hope this answers the question.