Question

Michael has a substance that he puts in Container 1. The substance has a volume of 5 cubic meters. He then puts the substance in Container 2, and it now has a volume of 10 cubic meters. In which phase(s) is the substance

Answer 1

Solids and liquids don't suddenly change their volumes.

But gases do ... they expand to fill whatever container you
put them in.

Michael's mystery substance is in the gaseous phase.