i dont think their are a exact number
Answer:
c. Cr
Explanation:

The compound is containing
ion.
If acid reacts with it, CO_2 evolves.

therefore, Cr would form a precipitate when added to an aqueous solution of this compound. Cr2CO3 is the precipitate.
It would be carbon dioxide codd2 for the molecules
Answer:
B
Explanation:
i hope this help but if it didn't tell me.
Answer:
Explanation: Zn (s) + 2 AgCl (s) ⇒ ZnCl2 (s) + 2 Ag(s)
Less noble Zinc reduces more noble Silver