Complex sentence: For example: the UV photolysis of mercury (I) chloride Hg 2 Cl 2 → Hg + HgCl 2 is a disproportionation since mercury (I) is both reduced to mercury (0) and oxidized to mercury (II).
Split into simpler sentences: For example: the UV photolysis of mercury (I) chloride Hg 2 Cl 2 → Hg + HgCl 2 is a disproportionation. In this reaction one mercury atom in the molecular ion is reduced to mercury (0) and the other is oxidized to mercury (II).