1) Alkali metals are stored in oil to minimise reaction with oxygen or water, it's a physical barrier towards air but the alkali metals still gradually corrode a traces of oxygen and water diffuse through. The reaction of alkali metals with water gets more violent for elements lower in the group e.g. (Li < Na < K < Rb < Cs). Adding them to water will cause an explosion due to the extremely exothermic nature of reaction, and can be rather dangerous and some alkali metals can react violently with just moisture in the air. Most of the alkali metals float on the top of the water, depending on how big the alkali metal is determines the size of the reaction this is because they're less dense that water itself and also during the reaction the alkali metals give of hydrogen gas which is quite flammable. Alkali Metal + Water » Metallic Hydroxide + Hydrogen
The francium would be like any other alkali metal, it would be very violent like the other alkali metals.