Relationship Between Given Stereoisomeric Structures

To determine the relationship between the two given 3D structures, let us analyze the central carbon atom and its attached groups:

1. Identify the attached groups:

   • Group 1: $-\text{Br}$ (Bromine)
   • Group 2: $-\text{Cl}$ (Chlorine)
   • Group 3: $-\text{CH}_3$ (Methyl group)
   • Group 4: $-\text{Me}$ (Methyl group)

2. Check for Chivalry:

   • The chemical designation $-\text{Me}$ stands for a methyl group ($-\text{CH}_3$).
   • Therefore, the central carbon atom is bonded to two identical methyl groups ($-\text{CH}_3$ and $-\text{Me}$).
   • A carbon atom is chiral (a stereocenter) only if it is bonded to four different atoms or groups. Since two of the four attached groups are identical, the central carbon atom is achiral.

3. Conclusion:

   • Because the molecule contains no chiral center, it possesses an internal plane of symmetry (passing through the $-\text{Br}$, $\text{C}$, and $-\text{Cl}$ atoms, bisecting the angle between the two methyl groups).
   • Any representation of an achiral molecule is superimposable on another representation of the same molecule.
   • Thus, both drawn structures represent the exact same achiral compound (1-bromo-1-chloroethane) and are identical molecules.

Correct Answer: B. identical molecules.