For a simple cubic lattice, the ratio between the unit cell length and the separation of two adjacent parallel crystal planes can NOT have a value of
(a)$5^{1 / 2}$
(b)$7^{1 / 2}$
(c)$111^{1 / 2}$
(d)$131^{1 / 2}$
Answer
Answer: B ✓ checked by 4AB · confidence high
Explanation
a/d = √(h² + k² + l²) must be the square root of a sum of three squares: 5 = 4+1+0, 11 = 9+1+1, 13 = 9+4+0 are possible, but 7 cannot be written as a sum of three squares.