**Answer:**

The unit cell edge length for the alloy is **0.405 nm**

**Explanation:**

Given;

concentration of Ag, = 78 wt%

concentration of Pd, = 22 wt%

density of Ag = 10.49 g/cm³

density of Pd = 12.02 g/cm³

atomic weight of Ag, = 107.87 g/mol

atomic weight of iron, = 106.4 g/mol

**Step 1:** determine the average density of the alloy

**Step 2:** determine the average atomic weight of the alloy

**Step 3:** determine unit cell volume

for a FCC crystal structure, there are 4 atoms per unit cell; n = 4

**Step 4:** determine the unit cell edge length

Vc = a³

= 0.405 nm

Therefore, the unit cell edge length for the alloy is **0.405 nm**