1. The problem statement, all variables and given/known data The element rubidium consists of two isotopes, the stable 85Rb and radioactive 87Rb (abundance 27.83%). What is the specific activity of natural rubidium chloride? Use Ar85.47 gmol-1 for rubidium element, Ar 86.91 gmol-1 for 87Rb, and Mr 120.92 gmol-1 for RbCl. 2. Relevant equations A2 = (λ2A1 /λ2-λ1) (e^-λ2 *t) M = (N#/ avag const)* Ar 3. The attempt at a solution I tried to convert 1g (subjective choice) of RbCl to 5 x 10^21 molecules, then apply percent abundance to get 1.4 x 10^21 Rb87. I converted that back to grams and got .2. I really don't know if I am on the right track or not, because I can't seem to figure out where I am going with this and if I need the other Ar value. Thanks.