A Level Chemistry OCR Practice Exam

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How is a compound formed?

From elements with varying ratios
From two or more chemically bonded elements in a fixed ratio
From just one type of atom
From solid minerals only

The correct answer is: From two or more chemically bonded elements in a fixed ratio

A compound is formed specifically from two or more chemically bonded elements that are combined in a fixed ratio. This ratio is determined by the nature of the elements involved and their tendency to combine in certain ways. For example, in water (H₂O), hydrogen and oxygen are bonded in a 2:1 ratio, meaning that for every two hydrogen atoms, there is one oxygen atom. This fixed ratio is crucial in defining the unique properties of the compound, including its chemical behavior and how it interacts with other substances. The idea of a compound being made from varying ratios or just one type of atom does not accurately reflect the definition of a compound. Compounds consist of different elements combined together, unlike elements, which are pure substances made of a single type of atom. Similarly, the notion that compounds are formed solely from solid minerals excludes many compounds that are liquid or gaseous, further emphasizing that a compound is defined by its chemical composition and bonding rather than its physical state.