How you know oxidation state of rubidium is 1?

Answer 1

Chemists observe the ratio with which a given element combines with other elements. That is how all the conclusions about oxidation states are derived. Since we also have data on the atomic weight of elements, we can weigh a given sample and know how many moles it contains. If one mole of rubidium combines with one mole of chlorine, we can conclude that rubidium has an oxidation state of 1, combining evenly with chlorine, which has an oxidation state of minus one. Millions and millions of different chemical reactions have been observed, and all this observation has been analysed to determine what the elements are actually doing.