Answer
a) $2HgO\rightarrow 2Hg + O_2$
b) $2H_2O_2\rightarrow 2H_2O + O_2$
c) $2KClO_3\rightarrow 2KCl + 3O_2$
Work Step by Step
All of these compounds undergo thermal degradation with the evolution of oxygen:
a) $2HgO\rightarrow 2Hg + O_2$
b) $2H_2O_2\rightarrow 2H_2O + O_2$
c) $2KClO_3\rightarrow 2KCl + 3O_2$