Which is the best example of a pure substance?

Study for the North Carolina Grade 8 End-of-Grade Science Test. Prepare with multiple choice questions, each question has hints and explanations. Ace your exam!

Multiple Choice

Which is the best example of a pure substance?

Explanation:
Pure substances have a single kind of particle and a definite composition. Gold fits this because it is an element—every bit of gold is made of gold atoms, so its composition is the same throughout. You can change its appearance or state (shape, melt it, etc.), but you’re not creating new substances from it through physical means. The other items are mixtures: peanuts contain many ingredients, milk has water, fats, and proteins, and air is a mix of several gases. Because they’re mixtures, their composition isn’t uniform. So gold is the best example of a pure substance.

Pure substances have a single kind of particle and a definite composition. Gold fits this because it is an element—every bit of gold is made of gold atoms, so its composition is the same throughout. You can change its appearance or state (shape, melt it, etc.), but you’re not creating new substances from it through physical means. The other items are mixtures: peanuts contain many ingredients, milk has water, fats, and proteins, and air is a mix of several gases. Because they’re mixtures, their composition isn’t uniform. So gold is the best example of a pure substance.

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