Question

how to find calcium carbonate formula

Answer 1

calcium carbonate
         
                            Ca         Co
                              3           1          
          
  By cross multiplication it will be : CaCo₃

Answer 2

since the valency of calcium is 2+ and carbonate is also 2-, so by exchanging their valency we get ca2(co3)2
cuttind down the common no. 2 from both the radicals we get the formula caco3(ignoring their signs)