Answer : Precipitation reactions occur when particular species of cations and anions in an aqueous solution combines to form an insoluble ionic solid which can be called as precipitate.
Here, the anions that will mostly form precipitate with [tex] Ca^{+2} [/tex] are OH anions, Cl ions, Br ions, [tex] SO_{4} [/tex] ions, [tex] C_{2} H_{3} O{2} [/tex] ions.
Calcium has valency of 2 electrons in its valence shell. So, any anion that can satisfy the valency of calcium can form a compound with calcium.
