🤓 Based on our data, we think this question is relevant for Professor Sun's class at KU.
To solve this problem, we will need to calculate the packing efficiencies of both unit cells.
The first unit cell is a face-centered cubic unit cell as we see that there are 8 corner atoms and 6 face atoms.
Recall that packing efficiency is the percentage of occupied space in the unit cell.
As molten iron cools to 1674 K, it adopts one type of cubic unit cell; then, as the temperature drops below 1181 K, it changes to another, as depicted below:
Which crystal structure has the greater packing efficiency?