Why is robidium Rn more reactive than potassium k?

Rubidium is a typical but very reactive member of the series of alkali metals. It is appreciably more reactive than potassium, but less so than caesium, and so would be expected to react more violently with those materials that are hazardous with potassium or sodium. Alkali metals have one valence electron in their outermost shell and can easily lose it and therefore, they are highly reactive. Rubidium is more reactive than potassium because the atomic radius of rubidium is larger than potassium so the valence electron experiences less attractive force from the nucleus and can easily be lost. Thus, rubidium get rids of electron easily.

the product of the pressure and volume is also constant