What term describes substances that have the same combination of elements but are arranged spatially in different ways?

The term that describes substances with the same combination of elements arranged spatially in different ways is "isomer." Isomers are compounds that share a molecular formula but differ in the spatial arrangement of atoms, giving rise to different structural and sometimes functional properties. This phenomenon arises from the flexibility in the bonding and arrangement of atoms within a molecule.

The concept of isomerism is fundamental in chemistry, particularly in organic compounds, where slight changes in structure can result in vastly different chemical behaviors and characteristics. For instance, butane and isobutane are both C4H10 isomers but have different branching and properties due to the arrangement of their carbon skeletons.

Other terms provided in the options pertain to different concepts: alloys refer to mixtures of metals, isotopes involve variations of elements based on differing neutron counts, and compounds refer to substances formed from two or more elements chemically bonded together. Understanding isomers is crucial for studying chemical structures and reactivity in chemistry-related fields.