Use the References to access important values if needed for this question.

Which one of the following observations would demonstrate that a substance is an element?

Heating the substance causes it to melt, and then to boil.

It can be separated into simpler substances by physical methods.

It cannot be separated into simpler substances by physical methods, but it can be separated into simpler substances by chemical methods.

It cannot be separated into simpler substances by physical or chemical methods.