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 a slat and water are formed.
it reacts then gives off gases and releases a flame.
copper
Water
Hydrogen
rust
Metal hydroxide + hydrogen gas