The correct option is B CaCO3
CO2 dissolves in water to form carbonic acid.
CO2(g)+H2O(l)⟶H2CO3(aq)
Lime water, which is calcium hydroxide, neutralizes the carbonic acid. The product is calcium carbonate, an insoluble, white salt. Hence the milkiness of the solution.
H2CO3(aq)+Ca(OH)2(aq)⟶CaCO3(s)+2H2O(l)
Overall, this reaction can be represented as:
Ca(OH)2+CO2⟶CaCO3+H2O