Step 1: Write the reaction of \(CaCO_3\) with dilute HCl.
\[
CaCO_3+2HCl\rightarrow CaCl_2+CO_2+H_2O
\]
The three products formed are:
\[
CaCl_2,\ CO_2,\ H_2O
\]
Step 2: Identify the product passed into slaked lime.
Slaked lime is
\[
Ca(OH)_2
\]
Carbon dioxide reacts with slaked lime as:
\[
CO_2+Ca(OH)_2\rightarrow CaCO_3+H_2O
\]
Step 3: Identify \(X\).
The white precipitate formed is calcium carbonate:
\[
CaCO_3
\]
Step 4: Final conclusion.
Hence,
\[
\boxed{CaCO_3}
\]
is \(X\).