Nature of Matter: Elements, Compounds and Mixtures — Class 8 MCQs with Answers

Nature of Matter: Elements, Compounds and Mixtures — important questions & MCQs with answers (Class 8 Science)

6 solved questions from this chapter's difficulty levels, each with its answer and explanation. Tap an option to check yourself.

0 of 6 answered

1. Q1 of 6Easy

   A mixture is made of:

   Atwo or more substances mixed togetherBonly one substanceCa single atomDpure water only
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   Answer: two or more substances mixed together

   Explanation: A mixture forms when two or more substances are combined without any chemical reaction between them, so each substance keeps its own identity.

2. Q2 of 6Easy

   An element is a pure substance that:

   Ais a mixtureBis made of many substancesCcannot be broken down into simpler substancesDis always a gas
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   Answer: cannot be broken down into simpler substances

   Explanation: An element is the simplest form of matter — it cannot be split into any simpler substance by ordinary physical or chemical means.

3. Q3 of 6Medium

   Water can be broken into hydrogen and oxygen by an electric current, which shows water is a:

   AcompoundBelementCmixtureDsingle atom
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   Answer: compound

   Explanation: Water can be broken into hydrogen and oxygen through electrolysis, and only a compound can be split into simpler substances this way — an element cannot.

4. Q4 of 6Medium

   To separate iron filings from a sand-and-iron mixture, you use:

   Aa magnetBevaporationCa batteryDa lens
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   Answer: a magnet

   Explanation: A magnet attracts the magnetic iron filings out of the mixture, leaving the non-magnetic sand behind.

5. Q5 of 6Hard

   Which of these is NOT a pure substance?

   AoxygenBwaterCsalt waterDiron
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   Answer: salt water

   Explanation: Salt water is a mixture with variable composition, while oxygen, water and iron are all pure substances — elements or compounds.

6. Q6 of 6Hard

   Which list contains only elements?

   Airon, oxygen, copper, sulfurBwater, salt, ironCair, oxygen, ironDsugar, water, oxygen
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   Answer: iron, oxygen, copper, sulfur

   Explanation: Iron, oxygen, copper and sulfur are each made of only one kind of atom, so all four are elements; the other lists mix in compounds like water and salt.

Nature of Matter: Elements, Compounds and Mixtures notes: key concepts (Class 8 Science)

This chapter classifies all matter. A mixture is two or more substances simply mixed together — its components keep their own properties, can be in any proportion, and can be separated by physical methods. A pure substance has just one kind of particle and is either an element or a compound. Elements are the simplest substances (one kind of atom, metals/non-metals/metalloids) and cannot be broken down. Compounds form when elements combine chemically in a fixed ratio to make a new substance with new properties, separable only by chemical means — as the iron-and-sulfur experiment neatly shows.

Mixture

Two or more substances mixed together whose components keep their own properties, are not chemically combined, and can be present in any proportion.

Components of a mixture

The individual substances that make up a mixture; they can be separated from one another by physical methods.

Pure substance

Matter made of only one type of particle, so all its particles behave identically; it is either an element or a compound.

Element

The simplest kind of pure substance, made of a single kind of atom, which cannot be broken down into anything simpler — the building block of all matter.

Metals, non-metals, metalloids

Elements are classified as metals (iron, copper, aluminium), non-metals (carbon, sulfur, hydrogen, oxygen) or metalloids, whose properties lie in between.

Compound

A pure substance formed when two or more elements combine chemically in a fixed ratio, giving a new substance with properties different from its elements.

Fixed ratio

The elements in a compound are always in a fixed ratio — hydrogen to oxygen in water is 2:1 and sodium to chlorine in common salt is 1:1.

New properties of a compound

A compound's properties differ from its elements: sodium (a reactive metal) and chlorine (a poisonous gas) form safe, tasty common salt.

Mixture versus compound

Iron filings and sulfur mixed can be separated by a magnet, but heating them forms iron sulfide, a compound the magnet cannot affect — a mixture is separable physically, a compound is not.

Separating mixtures

Choose a method to match a property: a magnet for iron, evaporation for dissolved salt, filtration for insoluble solids, and handpicking for large impurities.

Alloys and minerals

An alloy is a mixture of metals (like brass); a mineral is a natural solid with a fixed composition, usually a compound but occasionally a pure element.