Mercury(II) oxide HgO decomposes to form mercury Hg and oxygen open paren cap o sub 2 close paren The balanced chemical equation is shown. 2 HgO rightarrow 2 Hg plus cap o sub 2 The molar mass of cap o sub 2 is 32 point 0 0 g over mol How many moles of HgO are needed to produce 250 point 0 g of cap o sub 2 ?

First convert oxygen mass to moles: 250.0 g ÷ 32.00 g/mol = 7.8125 mol O₂. The balanced equation shows that 2 mol HgO produce 1 mol O₂, so the required HgO is 2 × 7.8125 = 15.625 mol, or 15.63 mol to four significant figures. The correct choice is 15.63 moles.

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