In a science demonstration, a teacher mixed zinc (Zn) with hydrogen chloride (HCl) in a flask and quickly attached a balloon over the mouth of the flask. Bubbles formed in the solution and the balloon inflated.

Zinc reacts with hydrogen chloride (hydrochloric acid) in a chemical reaction: Zn + 2HCl → ZnCl₂ + H₂. The bubbles and inflating balloon indicate that hydrogen gas formed, and zinc chloride is also produced in the solution. Because one or more new substances formed, choice D is correct.

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