Here's why:
* Rubidium (Rb) is an alkali metal. Alkali metals typically form +1 ions (Rb⁺).
* 20 is a very high number for a compound. Compounds usually have a relatively small number of atoms in their formula.
It's highly unlikely that rubidium would form a stable compound with 20 atoms.
If you are referring to a different compound, please provide more information!
