Calcium and its compounds, have properties typical of Group 2 in the Periodic Table.
Calcium carbonate, CaCO3, reacts with acids such as nitric acid.
A student neutralised 2.68 g of CaCO3 with 2.50 mol dm–3 nitric acid, HNO3. The equation for this reaction is shown below.
CaCO3(s) + 2HNO3(aq) → Ca(NO3)2(aq) + CO2(g) + H2O(l)

This is the full question, I know the molar ratio is 0.00268 moles of CaCO3 neutralises 0.00536 moles of HNO3