Answer :
the formula for calcium hydrogen carbonate is Ca(HCO3)2.
there is a 2 on the outside because calcium has a +2 charge and carbonate has a -1 charge, so in order to make the formula true, you have to “criss cross” the charges down
there is a 2 on the outside because calcium has a +2 charge and carbonate has a -1 charge, so in order to make the formula true, you have to “criss cross” the charges down