What coefficient does HCl have in the following balanced equation CaCl2 plus H2CO3CaCO3 plus HCl?

The coefficient of HCl in the balanced equation is 2. This is because the balanced equation shows that 1 molecule of CaCl2 reacts with 1 molecule of H2CO3 to form 1 molecule of CaCO3 and 2 molecules of HCl.