Copper metal has a face-centred cubic structure with the unit-cell length equal to 0.361 nm. Picturing copper ions in contact along the face diagonal, what is the apparent radius of a copper ion?

Explanation

To find the apparent radius of a copper ion in a face-centered cubic (FCC) structure, we can follow these steps:

### Step 1: Understand the Face-Centered Cubic Structure
In a face-centered cubic (FCC) unit cell, there are atoms located at each corner of the cube and one atom at the center of each face. When considering the face diagonal, there are three atoms involved: one at each corner and one at the center of the face.

### Step 2: Identify the Face Diagonal Length
The length of the face diagonal (d) in a cubic unit cell can be calculated using the formula:
\[ d = \sqrt{2} \times a \]
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