`CaCO_3` molar mass = 100g/mol
Moles in 10g of `CaCO_3 = 10/100 = 0.1 mol`
Atoms in 1 mol of `CaCO_3 = 6.022xx10^23`
Atoms in 0.1 mol `CaCO_3 = 0.1xx6.022xx10^23 = 6.022xx10^22`
We have similar amount of Ca and C atoms.
Amount of Ca moles in 10g of `CaCO_3 = 0.1`
Mass of carbon in 0.1mol of `CaCO_3 = 40xx0.1 = 4g`
Non of the answers are correct.