Final answer:
The correct PD expression for the (100) plane in an FCC crystal structure is Option A: (100): 1 layer, 0 in between, which shows that there's only one layer of atoms on the (100) plane without any additional layers between them.
Step-by-step explanation:
The PD (Planar Density) expression for the (100) plane in a Face-Centered Cubic (FCC) crystal structure refers to the arrangement and number of atom layers when looking at the crystal from that plane.
In the FCC structure, also known as Cubic Closest Packing (CCP), atoms are arranged as closely as possible and the structure is composed of three repeating layers of hexagonally arranged atoms, which follow an ABC packing sequence.
However, when observing the (100) plane specifically, you will notice a different pattern. The (100) plane cuts through the corners of the cubic unit cell, where atoms are at the corners and one atom is at the face center on the plane.
This results in a single layer of atoms without additional atoms in between. This can be visualized by seeing atoms at each corner of the square face of the cube, with a single atom in the middle of this face. Therefore, the correct PD expression for the (100) plane in FCC is:
Option A: (100): 1 layer, 0 in between. This indicates that there is only one layer of atoms on the (100) plane with no layers in between.