Question

is the compound soluble or insoluble in water? rboh

Explanation:

According to solubility rules, hydroxides ($\ce{OH-}$) of Group 1 elements (alkali metals) are soluble in water. Rubidium ($\ce{Rb}$) is a Group 1 element. So, $\ce{RbOH}$ (rubidium hydroxide) will dissolve in water.

Answer:

soluble (aq)