First of all we need the formula for Calcium Carbonate which is as follows:

Ca

Therefore Calcium Carbonate is expressed as CaCO

The answer is 3 Oxygen atoms are present in this formula.

Ca

^{2+}Plus one Carbonate ion which is CO_{3}^{2-}, please note that the oxidation state of the Carbonate ion is 2-, therefore Ca and the Carbonate ion are balanced as far as oxidatio or charge is concerned.Therefore Calcium Carbonate is expressed as CaCO

_{3}, now we are in a position to calculate the no. Of Oxygens's in calcium carbonate. We see that Oxygen has a subscript of 3 indicating the no. Of Oxygen atoms present, therefore we have 3 Oxygen atoms present in CaCO_{3}. As we see we must balance for charge before we are in a position to answer the question.The answer is 3 Oxygen atoms are present in this formula.