Silver (Z = 47), copper (Z = 29), and platinum (Z = 78) can be used as the target in an X-ray tube. Rank in descending order (largest first) the energies needed for impinging electrons to knock a K-shell electron completely out of an atom in each of these targets.
(a) Silver, copper, platinum
(b) Silver, platinum, copper
(c) Platinum, silver, copper
(d) Platinum, copper, silver
(e) Copper, silver, platinum