Which is the most accurate description of compounds? Select one: a. They have a unique set of properties that can be used as identifiers. b. They cannot be broken down into the elements that form them through chemical changes. c. They are formed by elements that join in any given mass ratio. d. They have the same properties as the elements that make them up.

The sentence, which most accurately describe compounds is this: THEY HAVE A UNIQUE SET OF PROPERTIES THAT CAN BE USED AS IDENTIFIERS.
Compounds are formed when two or more elements combine together in a specific mass ratio. Compounds normally have some properties which can be used to identify them. For instance, water as a compound has the following physical properties: it is odorless, colorless, neutral to litmus paper, it is a liquid at room temperature, it has a boiling point of 100 degree Celsius and a freezing point of zero degree Celsius. All these properties can be used to identify water in case it is given to us as an unknown substance. If the unknown substance does not have all these properties, then it is not water.