Question

in the following unit cell, which vector represents the 121 direction?
a
b
c
d

Explanation:

Step1: Recall Miller - indices concept

Miller - indices [uvw] represent a direction in a unit - cell. The components u, v, and w are the number of unit - cell edge lengths traversed in the x, y, and z directions respectively.

Step2: Analyze each vector

For vector A: It has a non - standard set of displacements in the x, y, z directions that do not match [121].
For vector B: Consider the displacements from the origin to the end - point of the vector. If we assume the unit - cell edge lengths as the reference, the displacements in x, y, z directions are consistent with [121].
For vector C: Its displacements in the x, y, z directions do not match [121].
For vector D: Its displacements in the x, y, z directions do not match [121].

Answer:

B. Option B