What type of reaction is #HgO -> Hg + O_2#?
Reddish Mercury(II)oxide solid is decomposed (broken down) upon heating into silver liquid mercury and colourless oxygen gas.
The full balanced chemical equation is
This is a decomposition reaction.
Because mercuric oxide is fairly stable, you have to heat it fairly fiercely. You end up with a test tube where mercury metal condenses on the top of the test tube. Of course, this reaction is performed in an efficient fume hood, because you don't want to inhale mercury metal. The decomposition reaction of cinnabar, mercuric sulfide,