What type of isomerism occurs when compounds have the same molecular formula but different arrangements of atoms?

The correct answer pertains to structural isomerism, where compounds possess the same molecular formula but differ in the connectivity of their atoms. Structural isomers can vary in the order in which atoms are bonded to each other, leading to distinct compounds with different properties. This type of isomerism encompasses variations in functional groups, carbon skeletons, or the positions of substituents on a carbon chain.

For instance, butanol, which has the molecular formula C4H10O, can exist as several structural isomers, including n-butanol and isobutanol, demonstrating that the same set of atoms can be connected in different ways to create diverse molecules.

The other types of isomerism listed focus on different aspects. Stereoisomerism refers to isomers that differ in the spatial arrangement of atoms but maintain the same connectivity, while geometric isomerism is a subset of stereoisomerism characterized by restricted rotation around double bonds. Conformational isomerism specifically deals with the different spatial arrangements of atoms that occur due to rotation around single bonds, which does not involve a change in connectivity. Thus, these distinctions clarify why structural isomerism is the answer that best fits the description provided in the question.