calculate mass of each of the following
8.22x10^23 what, exactly? Moles of rubidium, atoms of rubidium? I’m assuming it’s atoms, so If you are given 8.22x10^23 atoms of rubidium, all you need to find the mass is Avogadro’s number (6.022x10^23 atoms per mole of given substance) and the molar mass of rubidium (found on your periodic table). Using dimensional analysis, multiply 8.22x10^23 atoms of rubidium by (1 mole rubidium ÷ 6.022x10^23 atoms rubidium), essentially the same as dividing by 6.022x10^23 to cancel out the unit: atoms rubidium. Now your answer is in the unit of moles rubidium. Multiply this answer by the molar mass of rubidium (unit g/mol) to cancel out moles of rubidium. Now you are left with an answer in grams.
Here’s a picture of my work (on imgur, no worries)