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A 0.543 g sample of copper oxide is heated in a properly prepared crucible. Its final mass after heating is 0.519 g.
Which of the following is the BEST explanation for this change in mass?
The crucible was not completely cooled when weighed.
The sample was improperly stored while cooling, causing moisture to be absorbed by the copper oxide.
The copper oxide decomposed and oxygen gas was produced.
Black soot appeared on the crucible while heating, changing the masses obtained in the lab.