<span>Answer : The average atomic mass of rubidium = 85.468
Explanation: Given that 85Rb isotope has atomic mass of 84.912amu with abundance of 72.17%
therefore we get 84.912 x 0.7217 = 61.281
and 87Rb isotope has atomic mass of 86.909 with abundance of 27.83%
hence we get 86.909 x 0.2783 = 24.187
Thus we get 61.281 + 24.187 = 85.468 as the average atomic mass of Rubidium.</span>
Becouse melting point and cooling point are two opposite things one is 100degrees nd other 0degrees