@shogun. CaCO3= 40+12+16+16+16= 100
Number of moles of CaCO3 = 0.3/100= 0.003
Number of moles of HCL = 1 mol per dm3, and 1000cm3 = 1 dm3. 5/1000= 0.005
The reaction needs 1 mol of CaCO3 and 2 mols of HCl. So the HCl needs to be double the the CaCO3, but here there isnt enough, because the CaCO3 is 0.003, and the HCl needs to be 0.006, but its only 0.005. So CaCO3 is in excess.
I was kinda confused myself doing the question. Check with the mark scheme and tell me if im correct. If i am, +rep me PLZ. I REALLY NEED IT!!