Copper has the FCC structure with a lattice parameter of 0.3615 nm and a molar mass of 63.55 g/mol. Taking Avogadro's number as 6.022×10²³ mol⁻¹, which value is closest to the calculated density of copper?

Answer: C. About 8.94 g/cm³

The density is ρ = nM/(N_A a³), and the FCC unit cell contains n = 4 atoms. With a = 0.3615 nm = 3.615×10⁻⁸ cm, a³ ≈ 4.724×10⁻²³ cm³, so ρ = 4 × 63.55 / (6.022×10²³ × 4.724×10⁻²³) ≈ 8.94 g/cm³, in good agreement with the measured value of about 8.96 g/cm³. About 2.23 g/cm³ is calculated with n = 1 (treating it as SC), and about 4.47 g/cm³ with n = 2 (treating it as BCC). The conversion from nm to cm (1 nm = 10⁻⁷ cm) is also a common slip, so make the units consistent before cubing.