Silver crystallizes in face-cantered cubic structure. The 2nd order diffraction angle of a beam of X-ray $(\lambda=1 \AA)$ of (111) plane of the crystal is $30^{\circ}$. Therefore, the unit cell length of the crystal would be
(a)$\mathrm{a}=3.151 \AA$
(b)$\mathrm{a}=3.273 \AA$
(c)$\mathrm{a}=3.034 \AA$
(d)$\mathrm{a}=3.46 \AA$
Answer
Answer: D ✓ checked by 4AB · confidence high
The source book printed C; on checking, D is correct — see the explanation.
Printed C; a = d111 × √3 = 3.46 Å.
Explanation
nλ = 2d sin θ with n = 2: 2 × 1 = 2d × 0.5 ⇒ d₁₁₁ = 2 Å; a = d√3 = 3.46 Å.