Final answer:
The crystal structure of iron is option 2 - body-centered cubic (BCC), with iron atoms occupying the eight corners of a cube along with one atom in the center. Each atom in the BCC structure has a coordination number of eight.
Step-by-step explanation:
The crystal structure of iron is the body-centered cubic (BCC) structure. In this structure, the unit cell of iron is cubic with atoms at all eight corners and a single atom at the center of the cube. Each corner atom is considered to be one-eighth of an atom because it is shared with adjacent unit cells, so there are effectively two atoms per unit cell. At temperatures below 910 °C, iron adopts this BCC crystal structure. The coordination number for an atom in BCC iron is eight, meaning each atom touches four atoms in the layer above and four atoms in the layer below.
In this crystal structure, iron atoms occupy the eight corners of a cube along with one atom in the center. Each atom in the body-centered cubic structure has a coordination number of eight. The BCC structure is one of the common forms in which metallic elements crystallize.