Which statement best describes the relationship between two molecules that have the same $\mathrm{molecular formula}$ but different $\mathrm{connectivity}$ of their atoms?

• A. They are tautomers.
• B. They are structural (constitutional) isomers.
• C. They are stereoisomers.
• D. They are identical compounds.

Answer: (B)

Verified step by step guidance

1. Understand the key terms: Molecular formula refers to the number and types of atoms in a molecule, while connectivity refers to how these atoms are bonded to each other.
2. Recognize that if two molecules have the same molecular formula but different connectivity, they differ in the way atoms are linked, not just in spatial arrangement.
3. Recall that structural (constitutional) isomers are compounds with the same molecular formula but different connectivity of atoms, meaning the bonds between atoms differ.
4. Differentiate this from stereoisomers, which have the same connectivity but differ in the spatial arrangement of atoms.
5. Conclude that the best description for molecules with the same molecular formula but different connectivity is that they are structural (constitutional) isomers.