Science · Matter and substances
Two descriptions of a material can answer different questions. Solid, liquid and gas describe states with different shape and volume behaviour. An elemental substance or a compound describes composition. Before comparing choices, decide which axis the question uses. Something can have a state and a composition at the same time.
This guide stays with the ordinary conditions and basic classification of the examples. Read almost constant volume as a description at those conditions, rather than a promise about every possible pressure or temperature. For a composition question, use the types of elements involved instead of deciding from the material’s appearance.
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A liquid takes the shape of its container while retaining an almost constant volume under the conditions of the example. Shape changing with the container does not by itself mean that the liquid fills every available volume. Check both shape and volume when choosing among solid, liquid and gas.
You can review the choice by writing two short labels beside it: what happens to shape, and what happens to volume. Do not substitute a colour, a container name or a familiar everyday use for those two properties.
An elemental substance is a pure substance containing only one chemical element. A compound contains elements chemically combined. Water, H₂O, is a compound containing hydrogen and oxygen; its liquid state under familiar conditions does not settle that composition classification.
The state question and the composition questions therefore call for different evidence. In one, compare shape and volume. In the others, compare the specified elemental composition. After the explanation, identify which words in the prompt told you which comparison to make. A name that sounds familiar can still belong to the wrong axis.
TRY & READ
Compare the choices before opening the answer and explanation. Reading an example does not save a test answer or score.
Example 1 · Chemistry: substances and separation
Answer: Liquid
A liquid flows and is usually difficult to compress.
Basic facts and equations in this chapter concerning matter, atoms, reactions, or equilibrium. The questions, choices, and explanations were independently authored.
Source checked: 2026-10-03Example 2 · Chemistry: substances and separation
Answer: An elemental substance
Oxygen and copper are examples containing only one type of element.
Basic facts and equations in this chapter concerning matter, atoms, reactions, or equilibrium. The questions, choices, and explanations were independently authored.
Source checked: 2026-10-03Example 3 · Chemistry: substances and separation
Answer: A compound
Water contains the chemically bonded elements hydrogen and oxygen.
Basic facts and equations in this chapter concerning matter, atoms, reactions, or equilibrium. The questions, choices, and explanations were independently authored.
Source checked: 2026-10-03Source checked: 2026-10-04
Topics: Chemistry: substances and separation. Range: Everyday knowledge, Broader knowledge. Difficulty: Basic, Standard. These are selected initially. You can change these on the setup screen.
Try this topic in a quizA test shows explanations after submission. Continuous challenge explains each answer. Review uses unresolved mistakes recorded on this device. Casual mode does not update learning records.