The temperature of something.
In exactly 1 mol Hg₂(NO₃)₂ , there are 2 mol Hg, 2 mol N and 6 mol O.
Since the molecular formula of Hg₂(NO₃)₂ shows that for every mole of the substance, we have 2 moles of Hg, 2 moles of N and 6 moles of O.
So, in exactly 1 mol Hg₂(NO₃)₂ , there are 2 mol Hg, 2 mol N and 6 mol O.
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It is called a cycle because it is repetitive, therefore making it a cycle (or almost never ending)