Step 1: Understanding the Concept:
Chlorine reacts with dry slaked lime to form bleaching powder. It is a mixed salt of hypochlorite and chloride.
Step 2: Detailed Explanation:
\[ \text{Ca(OH)}_2 + \text{Cl}_2 \rightarrow \text{CaOCl}_2 + \text{H}_2\text{O} \]
The product has the formula \(\text{CaOCl}_2\), often written \(\text{Ca(OCl)Cl}\). The other formulae \(\text{CaO}_2\text{Cl}_2\) and \(\text{CaOCl}\) are not the product of this reaction. \(\text{CaCl}_2\) alone would form only if the hypochlorite part were absent.
Step 3: Final Answer:
The compound formed is \(\text{CaOCl}_2\), option (A).
Final Answer:
Bleaching powder, CaOCl2, forms.
\[ \boxed{\text{(A) }\text{CaOCl}_2} \]