дано

m(HgO) = 2.17 g

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V(O2)-?

2HgO-->2Hg+O2

M(HgO) = 217 g/mol

n(HgO) = m/M = 2.17 / 217 = 0.01 mol

2n(HgO) = n(O2)

n(O2) = 0.01 / 2 = 0.005 mol

V(O2) = n*Vm = 0.005 / 22.4 = 0.112 L

ответ 0.112 л