A 0.518 g sample of limestone is dissolved in HCl and then the calcium is precipitated as `Ca_(2)C_(2)O_(4)`. After filtering and washing the precipitate, it requires 40 mL of 0.25 N `KMnO_(4)` solution acidified with `H_(2)SO_(4)` to titrate it as,
`MnO_(4)^(-) + H^(+) + C_(2)O_(4)^(2-) to CO_(2) + Mn^(2+) + 2H_(2)O`
The percentage of CaO in the sample is :
A. 0.54
B. `27.1%`
C. 0.42
D. 0.84
