4.D1 Aluminum-lithium (Al-Li) alloys have been developed by the aircraft industry to reduce the weight and improve the performance of its aircraft. A commercial aircraft skin material having a density of 2.47 g/cm³ is desired. Compute the concentration of Li (in wt%) that is required. 4.1FE Calculate the number of vacancies per cubic meter at 1000°C for a metal that has an energy for vacancy formation of 1.22 eV/atom, a density of 6.25 g/cm³, and an atomic weight of 37.4 g/mol. (A) 1.49 x 1018 m-3 (B) 7.18 x 1022 m-3 (C) 1.49 x 1024 m-3 (D) 2.57 x 1024 m-3