Which of the following is characterized by existing at a discrete energy level?

Electrons always have discrete energy levels, no matter whether they are in isolated atoms, in a multi-atom molecule, or in an extended lattice of atoms in a solid. The difference among these cases are the sizes of the energy differences separating the different energy levels available to the electrons in the system. 

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