To determine the percent composition of calcium oxide CaO in the limestone sample, we will use the mass balance calculations. Let's assume the student has provided the following data:Mass of limestone sample m_limestone = x gramsMass of carbon dioxide evolved m_CO2 = y gramsMass of calcium oxide left behind m_CaO = z gramsLimestone is primarily composed of calcium carbonate CaCO3 . When it is heated, it undergoes a decomposition reaction to form calcium oxide CaO and carbon dioxide CO2 :CaCO3 s CaO s + CO2 g Using the law of conservation of mass, the mass of the limestone sample should be equal to the sum of the masses of the products formed:m_limestone = m_CaO + m_CO2Now, we have the mass of calcium oxide m_CaO and the mass of the limestone sample m_limestone . To find the percent composition of calcium oxide in the limestone sample, we can use the following formula:Percent composition of CaO = m_CaO / m_limestone 100%Plug in the given values:Percent composition of CaO = z / x 100%Now, calculate the percent composition using the provided values for z and x.