Plutonium (atomic mass $=244\,\mathrm{g\,mol^{-1}}$) crystallizes in monoclinic lattice ($\mathrm{a=620\,pm}$, $\mathrm{b=480\,pm}$, $\mathrm{c=1100\,pm}$; $\beta=102^{\circ}$) with 16 atoms per unit cell. The density in $\mathrm{g\,cm^{-3}}$ will be close to (Use $\sin\beta=0.98$; $\sin(\beta/2)=0.78$)
(b)16.12
(a)25.38
(c)12.69
(d)20.26
Answer
Answer: D ✓ checked by 4AB · confidence high
Explanation
V = abc sinβ = (6.2 × 4.8 × 11.0)×10⁻²⁴ cm³ × 0.98 = 3.21×10⁻²² cm³; m = 16 × 244/6.022×10²³ = 6.48×10⁻²¹ g; ρ ≈ 20.2 g cm⁻³ (d).