Choose the composition of matter or compositions of matter that match each description.

Is a pure substance.

Mixture that is uniform in composition.

A uniformly colorless gas that breaks down into smaller particles at $94$ degrees Celsius.

Can be broken down by physical means.

Is a pure substance that cannot be broken down by chemical means.

A clear, colorless liquid that boils at $78$ degrees Celsius and then again at $100$ degrees Celsius.

A liquid that has a dark blue layer sitting above a dark brown layer.

A clear, colorless gas that condenses into a liquid at $25$ degrees celcius. In solid form, this substance will decompose into two different elements.