Chemical classification – What do we call a substance formed by chemically combining different elements in fixed proportions?

Introduction / Context:
Distinguishing elements, compounds, molecules, and mixtures is a foundational chemistry competence. This classification influences properties, separation methods, and reaction behavior.

Given Data / Assumptions:

• The material contains two or more different elements.
• Combination is chemical, forming a new substance with fixed composition.

Concept / Approach:
A compound is a pure substance made when elements chemically bond in definite ratios, producing properties different from the constituent elements. A molecule is a structural unit that can represent either an element (e.g., O2) or a compound (e.g., H2O). A mixture combines substances physically without fixed ratios and without chemical bonding.

Step-by-Step Solution:
Identify whether the description implies chemical bonding and fixed composition.Chemical bonding in fixed ratios leads to the term compound.Select the option stating compound.

Verification / Alternative check:
Water is a compound of hydrogen and oxygen in a 2:1 ratio by atoms. Brass is a mixture (alloy) of copper and zinc with variable composition, confirming the compound versus mixture distinction.

Why Other Options Are Wrong:

• Element: consists of one type of atom.
• Ion: an atom or molecule with net charge.
• Molecule: structural term that may not imply different elements or fixed stoichiometry when used alone.
• Mixture: lacks chemical bonding and fixed ratio.

Common Pitfalls:
Calling any multi-atom species a compound; remember molecules of an element exist (e.g., N2) that are not compounds.

Final Answer:
A compound