Answer:
Here we’ll use atomic mass and atomic volume.
Iridium density, p=m/v,
for a BCC crystal, 2atoms/a³ = Nₐ atoms/Vₓ,, Na=avogadro constant =6.02 x 10²³ atoms,
therefore, Atomic Volume, Vₓ = 6.02 x 10²³ (314x10⁻⁸)³/2 cm³ = 9.319x10⁶cm³
Density of Iridiumβ, ρ = Atomic mass / Atomic Volume = 192.21g/9.319x10⁶cm³
2.06 x 10⁻⁵g/cm³ to 3s.f