$$2HCl + CaCO_3 \rightarrow CaCl_2 + CO_2 + H_2O$$
From the equation, we can see that 2 moles of HCl are required to react with 1 mole of CaCO3.
To calculate the number of moles of HCl consumed, we need to first calculate the number of moles of CaCO3 present in the 25 mL of 4 M solution.
The number of moles of CaCO3 in 25 mL of 4 M solution is:
$$Moles = Concentration \times Volume$$
$$Moles = 4 M \times 25 mL = 0.1 mol$$
Since 2 moles of HCl are required to react with 1 mole of CaCO3, the number of moles of HCl consumed is:
$$Moles = 2 \times 0.1 mol = 0.2 mol$$
Therefore, 0.2 moles of HCl are consumed in the reaction.
