Which statement describes how a chemical formula communicates composition of a compound?

Which statement describes how a chemical formula communicates composition of a compound?

• A. It lists the types and numbers of atoms present in one molecule.
• B. It shows the physical state of each element.
• C. It indicates energy levels of the atoms.
• D. It describes how elements combine to form isotopes.

Answer: (A)

The idea being tested is how a chemical formula communicates composition. A chemical formula communicates which elements are present and how many atoms of each are in one molecule or formula unit. For example, water written as H2O shows two hydrogen atoms and one oxygen atom in every molecule, conveying the exact makeup. The subscripts indicate counts, and the element symbols identify the types of atoms involved. The other statements don’t describe composition. A physical state symbol or context isn’t part of the basic formula itself, so it doesn’t communicate what the substance is made of. Energy levels are described by electron configurations or diagrams, not by the formula. Isotopes concern different masses and may require special notation, but a standard formula focuses on which elements and how many atoms, not on isotopic identity.

The idea being tested is how a chemical formula communicates composition. A chemical formula communicates which elements are present and how many atoms of each are in one molecule or formula unit. For example, water written as H2O shows two hydrogen atoms and one oxygen atom in every molecule, conveying the exact makeup. The subscripts indicate counts, and the element symbols identify the types of atoms involved.

The other statements don’t describe composition. A physical state symbol or context isn’t part of the basic formula itself, so it doesn’t communicate what the substance is made of. Energy levels are described by electron configurations or diagrams, not by the formula. Isotopes concern different masses and may require special notation, but a standard formula focuses on which elements and how many atoms, not on isotopic identity.