Susana heats up a sample of red crystals. While the sample is being heated, a gas is released and a blue powder is left after the heating. Is the sample of red crystals an element or a compound? Explain your answer.

Compound

Explanation:

Element is a pure substance which is composed of atoms of similar elements.It can not be decomposed into simpler constituents using chemical reactions.Example: Copper

Compound is a pure substance which is made from atoms of different elements combined together in a fixed ratio by mass.It can be decomposed into simpler constituents using chemical reactions. Example: water

Thus as it give that  the red sample on being heated, a gas is released and a blue powder is left after the heating. Thus the given sample is a compound.