Rubidium can be liquid at ambient temp, but only on a hot day given that its m.p. is about 40°C. It is a soft, silvery-white metallic element of the alkali metals group. It is one of the most electropositive and alkaline elements. It ignites spontaneously in air and reacts violently with water, setting fire to the liberated hydrogen. As so with all the other alkali metals, it forms amalgams with mercury. It alloys with gold, caesium, sodium, and potassium. It colours a flame yellowish-violet.