Except for rubidium and caesium,___
To find out which elements are exceptions to rubidium and caesium, you can refer to the periodic table. The periodic table organizes all known elements according to their atomic number and chemical properties.
Rubidium (Rb) and caesium (Cs) are both alkali metals, which belong to Group 1 of the periodic table. Group 1 elements typically have similar properties, such as being highly reactive and having one valence electron. As you mentioned that elements other than rubidium and caesium are of interest, we can look at the elements that follow them on the periodic table.
After rubidium and caesium, the next element is francium (Fr). Francium, like rubidium and caesium, is also an alkali metal. It is the second rarest naturally occurring element and highly radioactive.
So, except for rubidium and caesium, the next element in the periodic table that does not belong to the alkali metal group would be barium (Ba). Barium is an alkaline earth metal and is located in Group 2 of the periodic table.
Therefore, rubidium, caesium, francium, and barium are the relevant elements to consider when discussing exceptions to rubidium and caesium.