Equation for the reaction of rubidium with an Arrhenius base

No reaction.

Explanation:

An Arrhenius base (like NaOH) increases the concentration of hydroxide ions present in the solution.

If you add Rb to an aqueous solution of NaOH, you will get an explosion.

However, the Rb does not react with the OH^-. Instead, it reacts rapidly with the water.

2Rb + 2H2O → 2RbOH + H2

So much heat is generated that the hydrogen explodes:

2H2 + O2 → 2H2O