Which statement about a chemical equation is true?

• A. It always includes a phase label (solid, liquid, gas) for every substance.
• B. It shows the left side as products.
• C. It shows the right side as reactants.
• D. It shows reactants on the left and products on the right.

Answer: (D)

In a chemical equation, the substances that react are written on the left and are called reactants, while the substances produced are on the right and are called products; the arrow between them shows the direction of the change from reactants to products. This left-to-right layout helps you see what starts the reaction and what is formed, and keeping the equation balanced ensures the same number of atoms of each element appears on both sides, reflecting the conservation of mass. Phase labels (s, l, g, aq) are sometimes shown, but they’re not required for every substance, so a statement insisting every substance must have a phase label isn’t universally true. Saying the left side are the products or the right side are the reactants would reverse the reaction direction, which is not how these equations are written. So the standard arrangement—reactants on the left, products on the right—is the correct description.