Yes, a compound always has a definite chemical composition. A compound is a pure substance composed of two or more elements chemically combined in fixed proportions by mass. The chemical composition of a compound refers to the specific elements present in the compound and the relative amounts of these elements.

Unlike mixtures, where the composition can vary, compounds have a consistent and well-defined chemical composition. This composition remains the same regardless of the amount or origin of the compound. The fixed proportions of elements in a compound are determined by its chemical formula.

For example, the compound water (H2O) always contains two hydrogen atoms for every one oxygen atom. No matter where water is found or how much of it there is, this ratio of hydrogen to oxygen remains constant. The chemical composition of water is consistently two parts hydrogen and one part oxygen by mass.

Similarly, other compounds such as carbon dioxide (CO2), sodium chloride (NaCl), or sucrose (C12H22O11) have specific chemical compositions that define their molecular structures and properties.