Answer:
339 grams Rb
Explanation:
To find the final answer, you need to (1) convert atoms to moles (via Avogadro's number) and then (2) convert moles to grams (via molar mass from periodic table).
Molar Mass (Rb) = 85.468 g/mol
2.39 x 10²⁴ atoms Rb 1 mole 85.468 g
------------------------------- x ----------------------------- x -------------------- = 339 g Rb
6.022 x 10²³ atoms 1 mole
