Potassium is the only metal (alkali metal) where a flame is present. Lithium and sodium fizz but there is no flame. Caesium, francium and rubidium all explode on contact with water.
Potassium produces a lilac flame
I believe that you think to alkali metals (ex. sodium).
Potassium has a violet color in the flame test.
Potassium and dont try it at home it is dangerous
The Rubidium valance shell is a radio active substance
When a metal oxide reacts with an acid, it produces a salt and water. The metal oxide will neutralize the acid by forming water, and the metal ion in the oxide will combine with the non-metal ion from the acid to form the salt. For example: iron(III) oxide reacting with hydrochloric acid produces iron(III) chloride and water.
it reacts then gives off gases and releases a flame.
copper
Water
When an alkali metal reacts with water, it produces an alkali metal hydroxide and hydrogen gas. This is a highly exothermic reaction, with the alkali metal displacing hydrogen from the water molecule.
rust
Metal hydroxide + hydrogen gas