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

C. They have a unique set of properties that can be used as identifiers.

Explanation:

In chemistry, compound is a clean substance comprised of two or more elements in a certain ratio.

Let's take an example of sodium chloride or NaCl, widely known as salt.

It is comprised of two elements, sodium and chlorine in a 1:1 ratio. If, for example, Na3Cl2 existed, it wouldn't be the same compound.

All compounds, using different methods, can be broken down to its basic elements. NaCl is broken down to sodium ion (Na⁺) and chloride ion (Cl⁻).

However, properties of a compound differ from those of its elements.

Sodium is silverish solid metal, chlorine is yellowish gas, and together they combine to give NaCl which is white and solid.

Based on their unique properties (do they dissolve in water or in some other liquid, their freezing temperature, characteristic smell, color, reactivity etc.) different compounds can be identified.