Compounds having the same molecular formula but different structural arrangements are known as:

The correct option is Isomers.

Explanation

In chemistry, the relationship between molecular formula and structural arrangement defines specific categories of substances. Isomerism is the phenomenon where two or more compounds possess the same molecular formula but differ in the arrangement of atoms (structural formula) and physical or chemical properties.

Option Analysis

• Isomers Isomers: Correct. Isomers are compounds that have the identical molecular formula (same number and types of atoms) but different structural arrangements. For example, n-butane and isobutane both have the molecular formula C₄H₁₀, but their atoms are connected differently.
• Isotopes Isotopes: Incorrect. Isotopes refer to atoms of the same element that have the same atomic number (number of protons) but different mass numbers (number of neutrons). This concept applies to elements, not compounds with different structures.
• Allotropes Allotropes: Incorrect. Allotropes are different physical forms in which the same element can exist. For example, diamond and graphite are allotropes of carbon. They are forms of an element, not necessarily compounds with the same molecular formula.
• Enzymes Enzymes: Incorrect. Enzymes are biological catalysts, primarily proteins, that accelerate chemical reactions in living organisms. This term relates to biological function rather than structural chemical classification.

Key Takeaway

Isomers are defined by the rule: Same Molecular Formula + Different Structural Formula. This distinction leads to differences in physical and chemical properties despite having the same atomic composition.