Which statement best describes a chemical change?

• A. gas
• B. new substance
• C. new element
• D. compound

Answer: (D)

When a chemical change happens, atoms are rearranged to form new substances with different properties. The best description here is that a compound is formed—a substance made from two or more elements bonded together in a fixed ratio, with properties distinct from the starting materials. A classic example is hydrogen and oxygen combining to make water, a compound that has its own characteristics unlike H2 or O2.

Why the other ideas aren’t as precise: a gas describes a state of matter, not the change itself, and chemical reactions can produce gases but that isn’t what defines the change. forming a new element is not typical in ordinary chemical reactions, since elements aren’t created by chemical means. And while a chemical change can yield a new substance in general, stating it as a compound captures the essential idea that chemical bonding creates a substance with a new composition.