Limewater

The answer is B.

A. Limewater contains WATER which will react with Calcium to form Calcium hydroxide & Hydrogen gas.

Ca (s) + 2H2O (l) --> Ca(OH)2 (s) + H2 (g) (solid Ca(OH)2 will be formed because limewater is saturated Calcium hydroxide solution)

C. White precipitate Iron (II) hydroxide will be formed.

FeSO4 (aq) + Ca(OH)2 (aq) --> Fe(OH)2 (s) + CaSO4 (aq)

D. Turns limewater milky i.e. test for Carbon dioxide

Ca(OH)2 (aq) + CO2 (g) --> CaCO3 (s) + H2O (l)

if more details and some references for the reactions are added, the answer will be better
like reaction of adding excess carbon dioxide into limewater, reason for forming precipitate and so on