Urgent chemistry question! How do I solve it?

Moin,

that is relatively simple but not unambiguous to answer.

More or less red flames produce the metals or salts of

• lithium,
• Rubidium,
• Calcium and
• Strontium.

Halogenides are usually shown with a silver nitrate solution. Included

• fluorides are not sufficient because they are water-soluble,
• chlorides as a white-cold precipitate,
• bromides as white-yellow, thick precipitate and
• Iodides as a yellow thick precipitate.

The tip that the “atom number ratio” in the salt amounts to 1:1 is unprecedented in a professional language because there are no uncharged atoms in the salt, but charged ions. Therefore, it should be called “ion ratio” in the tip. But well…
The tip tells you that it cannot be the salts of calcium or strontium. They would also have a reddish flame, but with halides no 1:1 but a 1:2 ratio.

The answer is:

The sought salt is either lithium chloride or rubidium chloride.

Chloride because bromides have white-yellow and iodides yellow precipitates in silver nitrate solutions.
Lithium or rubidium salts because on the one hand they agglomerate a red flame coloring, on the other hand only these two with chloride in a ratio of 1:1.

The reaction schemes (reaction equations) for the formation of salts from the elements are

Lithium chloride:
2 Li_(s) + Cl_2(g) → 2 LiCl_(s)

Rubidium chloride:
2 Rb_(s) + Cl_2(g) → 2 RbCl_(s)

LG from the Waterkant