Question

which of the following is not true of a compound?
a it has a unique composition that is always the same.
b the smallest particle of a compound is called a molecule.
c it is a substance that consists of two or more elements.
d it is always made up at least partly of carbon.

Explanation:

• Option a: Compounds have a fixed, unique composition (law of definite proportions), so this is true.
• Option b: For molecular compounds, the smallest particle is a molecule; for ionic compounds, it's a formula unit, but the statement is generally accepted in basic chemistry, so this is true.
• Option c: By definition, a compound is a substance made of two or more elements chemically combined, so this is true.
• Option d: Compounds like \(H_2O\), \(NaCl\) do not contain carbon. Only organic compounds (a subset of compounds) contain carbon, so this statement is not true of all compounds.

Answer:

d. It is always made up at least partly of carbon.