Ontario Grade 9 Science Class Practice Exam 2025 - Free Grade 9 Science Practice Questions and Study Guide

A compound is a pure substance that is formed by chemically joining two or more elements together in fixed ratios. Option A is incorrect because a mixture does not have fixed ratios and the components can be easily separated. Option B is incorrect because it states an element, which by definition cannot be a compound as it cannot be broken down into simpler substances. Option D is incorrect because a compound is not a product of a chemical reaction, but rather is formed through chemical bonding between elements.