When sugar is heated, it turns black because:

Sugar decomposes, leaving behind carbon (charcoal) and releasing water

Naturally occurring substances (elements or compounds) found in rocks

What is the difference between a mixture and a compound?

In a mixture, components retain properties and can be separated physically; in a compound, elements are chemically bonded in fixed ratios forming a new substance

In Activity 8.3 (passing electricity through water), hydrogen and oxygen were collected in different volumes. Why was hydrogen collected in a larger volume than oxygen?

Water is H₂O; hydrogen and oxygen are in a 2:1 ratio by atoms, so twice as much hydrogen gas is produced

The test tubes were different sizes

How can you identify hydrogen gas from Activity 8.3?

A pop sound is heard when a burning candle is brought near it

In Activity 8.5, Sample A (iron + sulfur mixture) is attracted by a magnet but Sample B (iron sulfide compound) is not. What does this demonstrate?

In a compound, the properties of constituent elements change; iron sulfide does not retain iron's magnetic property

The magnet is weak for compound

Hydrogen sulfide gas from iron sulfide reacting with hydrochloric acid smells like rotten eggs, while hydrogen gas from the same acid reacting with iron is odourless. What does this prove?

Iron and iron sulfide are the same substance

The compound (iron sulfide) has different properties from its constituent elements (iron and sulfur), confirming it is a compound

Why cannot the constituent elements of a compound be separated by physical methods?

In compounds, elements are chemically bonded in fixed ratios; only chemical methods can break these bonds

Physical separation is too slow

Air is a mixture, not a compound. Which fact from the chapter best supports this?

Nitrogen (78%) and oxygen can be identified separately in air; their properties are retained; air composition can vary

What is the purpose of separating mixtures in science?

To obtain pure substances from mixtures

Why does the chapter classify milk as impure from a scientific standpoint?

In science, a pure substance has only one type of particle; milk contains water, fat, protein and many other substances, so it is a mixture

What makes silicon and boron different from typical metals and non-metals?

They have intermediate properties between metals and non-metals and are called metalloids

In Activity 8.5, iron and sulfur are mixed in a 5.6g:3.2g ratio before heating. Why is this specific ratio used?

Iron and sulfur combine in a fixed mass ratio to form iron sulfide; using the exact ratio ensures complete reaction with no excess of either element

More iron makes it more magnetic

Random ratios work equally well

A student heats a mixture of iron and sulfur and forms a black compound. They then test both with a magnet and HCl. What combination of tests conclusively proves a compound was formed?

Both the magnet test (compound is non-magnetic) AND the gas test (compound produces rotten-egg H₂S, not odourless H₂ like the mixture)

Graphene aerogel is described as the lightest material made from carbon. It is highly porous. Why can it absorb oil spills efficiently?

Its extreme porosity provides a very large surface area and absorption capacity to trap oil within its structure

Cement is made from calcite, quartz, alumina, and iron oxide. These are minerals. What does this tell us about the relationship between minerals, compounds, and practical materials?

Many practical materials are mixtures of compounds (minerals); understanding chemistry of minerals helps engineers create materials with desired properties

The chapter explains that when sugar heats, carbon and water are produced. This shows sugar is a compound of which elements?

Carbon, Hydrogen, and Oxygen (water contains H and O; charcoal is carbon)

Two elements—sodium (a reactive metal) and chlorine (a toxic gas)—combine to form sodium chloride (common salt), which is harmless and edible. What general principle does this illustrate about compounds?

Compounds have entirely different properties from the elements that form them

Sodium and chlorine are found in table salt separately

Metals always form harmless compounds

The Dhokra art technique uses beeswax to model a shape, covers it in clay, melts the wax, and fills the cavity with molten brass. Which scientific concepts are demonstrated in this process?

Melting (wax), casting (liquid metal into mould), solidification—all using the particulate nature of matter and properties of mixtures (brass/alloys) and elements

Which of the following are examples of alloys (uniform mixtures of metals)? (Select all that apply)

Stainless steel (iron + nickel + chromium + carbon)

Which of the following correctly distinguish a compound from a mixture? (Select all that apply)

Compound components are chemically bonded in fixed ratios; mixture components are physically combined

A compound has different properties from its elements; a mixture retains properties of its components

Compounds cannot be separated by physical methods; mixtures can

Compounds are always uniform; mixtures are always non-uniform

Which of the following are properties of elements as described in the chapter? (Select all that apply)

Cannot be broken down into simpler substances

Include metals (gold, iron) and non-metals (oxygen, carbon) and metalloids (silicon, boron)

A student argues that mixing iron filings and sulfur (Sample A) is the same as making iron sulfide (Sample B) since both are black. Why is this argument flawed?

Sample A retains iron's magnetic property and produces odourless hydrogen gas with HCl; Sample B is non-magnetic and produces foul-smelling H₂S—proving they are fundamentally different substances

The colour difference proves it

A chemist uses solvents to extract compounds from medicinal plants (like Asima Chatterjee did). What does this tell us about the relationship between mixtures, compounds, and science?

All natural substances are pure elements

Plants contain mixtures of many compounds; scientists use solvents to separate and isolate specific compounds with medicinal properties—requiring deep understanding of mixtures and compounds

Plants contain no useful compounds

Manufacturing a mobile phone uses more than 45 elements including lithium, cobalt, gold, and silicon. What scientific implication does this have for sustainability?

Diverse elements must be mined globally; responsible sourcing, recycling, and substitution research are critical to sustainably manufacture and dispose of complex electronic devices

All these elements are abundant

Mobile phones can be made from one element

In science, a pure substance has only one type of particle, but in common usage 'pure' means unadulterated. How does this distinction matter in analysing food safety?

Food safety analysis requires knowing whether a food product contains adulterants (mixture), but scientific purity means checking for the presence of only one type of substance—more rigorous standards apply in food chemistry

Carbon exists as diamond and graphite, both pure carbon but with very different properties. Which of the following BEST explains why these are still called elements and not compounds?

They contain two types of atoms

Both are made of only carbon atoms; their differences arise from different arrangements of the same atoms—still the same element, just in different forms (allotropes)

Which of the following are ways that elements, compounds, and mixtures are used in everyday life as described in the chapter? (Select all that apply)

Air (mixture of gases) is what we breathe

Water (compound of H and O) is essential for life

Iron and aluminium (elements) are used in construction

Alloys like stainless steel (mixture of metals) are stronger than pure iron

Which of the following correctly describe tests to distinguish Sample A (iron+sulfur mixture) from Sample B (iron sulfide compound) in Activity 8.5? (Select all that apply)

Magnet attracts Sample A but not Sample B

HCl with Sample A produces odourless hydrogen; with Sample B produces foul H2S

Sample A shows both yellow sulfur and grey iron; Sample B is uniformly black

Sample A is non-magnetic; Sample B is magnetic

Which of the following correctly describe types of pure substances? (Select all that apply)

Elements are made of identical atoms and cannot be broken into simpler substances

Compounds are formed when elements bond chemically in fixed ratios

Pure gold, pure oxygen, and pure carbon are examples of elements

Water, sodium chloride, and sugar are examples of compounds

Which of the following correctly describe properties of minerals as described in the chapter? (Select all that apply)

Most rocks are mixtures of minerals

Native minerals are pure elements like gold, silver, sulfur

Most minerals are compounds of more than one element

Minerals are used in making cement, talcum powder, and other products

Which of the following correctly show how understanding elements, compounds, and mixtures has practical applications? (Select all that apply)

Chemists use this knowledge to create life-saving medicines

Engineers use alloy chemistry to design materials like stainless steel with special properties

Farmers benefit from knowledge of compounds (fertilisers) to improve crop production

Environmental scientists use microorganisms to clean compounds like oil from spills

NCERT Solutions Class 8 Science - Curiosity Chapter 8 – Nature of Matter: Elements, Compounds, and Mixtures

Name: Nature of Matter: Elements, Compounds, and Mixtures – Class 8 Science - Curiosity
Uploaded: 2026-07-23T08:07:13+00:00
Description: Everything around us is made of matter, which exists as elements, compounds, and mixtures. Elements combine chemically to form compounds, while mixtures are formed by physical combination of substances. Understanding matter helps us create useful materials, from alloys and medicines to everyday objects.

Class 8 Science - Curiosity

Last Updated: 23 July 2026

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Chapter Introduction

Everything around us is made of matter, which exists as elements, compounds, and mixtures. Elements combine chemically to form compounds, while mixtures are formed by physical combination of substances. Understanding matter helps us create useful materials, from alloys and medicines to everyday objects.

हिंदी में (Hindi)

हमारे आसपास की हर वस्तु पदार्थ से बनी है, जो तत्व, यौगिक और मिश्रण के रूप में पाई जाती है। तत्व मिलकर यौगिक बनाते हैं, जबकि मिश्रण पदार्थों के भौतिक संयोजन से बनते हैं। पदार्थ को समझना हमें उपयोगी वस्तुएँ जैसे मिश्रधातुएँ, दवाएँ और दैनिक उपयोग की चीज़ें बनाने में मदद करता है।

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Important Points

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Practice MCQ Questions (41 questions)

Q1. When two or more substances are mixed and each retains its own properties, it is called:

Q2. A mixture in which all components are evenly distributed and cannot be distinguished is called:

Q3. Elements are pure substances that:

Q4. A compound is formed when:

Q5. What are the two elements that make up water?

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Tough Words (Glossary)

matter

Meaning: Anything that has mass and takes up space.

अर्थ: द्रव्य/पदार्थ – वह जो द्रव्यमान रखता है और स्थान घेरता है।

"Everything you can touch is made of matter."

particle

Meaning: A very tiny piece of a substance.

अर्थ: कण – किसी पदार्थ का बहुत छोटा भाग।

"Water is made of tiny particles that move constantly."

mixture

Meaning: A combination of two or more substances where each keeps its own properties.

अर्थ: मिश्रण – दो या अधिक पदार्थों का मेल, जिसमें हर घटक अपने गुण बनाए रखता है।

"Lemonade is a mixture of water, sugar, and lemon juice."

component

Meaning: One of the parts that makes up a mixture.

अर्थ: घटक – मिश्रण का कोई एक भाग।

"Salt is a component of seawater."

ingredient

Meaning: A substance used to make a mixture or dish.

अर्थ: सामग्री/घटक – किसी मिश्रण या भोजन को बनाने में प्रयुक्त पदार्थ।

"Chickpeas are an ingredient in sprout salad."

dissolve

Meaning: To mix evenly in a liquid so that it seems to disappear.

अर्थ: घुलना – किसी द्रव में समान रूप से मिल जाना।

"Sugar dissolves in water to form a solution."

solution

Meaning: A uniform mixture formed when a solute dissolves in a solvent.

अर्थ: विलयन – वह समान मिश्रण जिसमें विलेय, विलायक में घुल जाता है।

"Salt solution conducts electricity."

uniform

Meaning: Evenly the same throughout; looks alike in all parts.

अर्थ: समान/एकरूप – हर भाग में एक जैसा।

"Air is a uniform mixture of several gases."

non-uniform

Meaning: Not the same throughout; different parts can be seen.

अर्थ: असमान/अनएकरूप – हर जगह एक जैसा नहीं; अलग भाग दिखते हैं।

"Sprout salad is a non-uniform mixture."

magnifying

Meaning: Making objects appear larger.

अर्थ: आवर्धक – वस्तुओं को बड़ा दिखाने वाला।

"A magnifying glass helps us see tiny particles."

alloy

Meaning: A uniform mixture of two or more metals (or metal with non‑metal).

अर्थ: मिश्र धातु – दो या अधिक धातुओं का एकरूप मिश्रण।

"Brass is an alloy of copper and zinc."

stainless steel

Meaning: A rust‑resistant alloy of iron with chromium and nickel.

अर्थ: स्टेनलेस स्टील – लोहे, क्रोमियम और निकेल की जंग‑रोधी मिश्र धातु।

"Many utensils are made of stainless steel."

brass

Meaning: An alloy of copper and zinc.

अर्थ: पीतल – ताँबा और जस्ता की मिश्र धातु।

"The bell is made of brass."

bronze

Meaning: An alloy of copper and tin.

अर्थ: काँसा/ब्रॉन्ज – ताँबा और राँगा (टिन) की मिश्र धातु।

"Ancient statues were cast in bronze."

composition

Meaning: What something is made of; the parts and their amounts.

अर्थ: संरचना/संघटन – किसी वस्तु के घटक और उनकी मात्रा।

"Air has a composition mainly of nitrogen and oxygen."

vapour

Meaning: The gaseous form of a substance that is liquid at room temperature.

अर्थ: वाष्प – ऐसी गैसीय अवस्था जो सामान्य ताप पर द्रव रहती है।

"Water vapour condenses on a cool surface."

combustion

Meaning: The process of burning.

अर्थ: दहन – जलने की प्रक्रिया।

"Oxygen supports combustion."

nitrogen

Meaning: A colorless gas that makes up about 78% of air.

अर्थ: नाइट्रोजन – रंगहीन गैस, वायु का लगभग 78%।

"Nitrogen does not support combustion."

oxygen

Meaning: A gas needed for breathing and burning.

अर्थ: ऑक्सीजन – श्वसन और दहन के लिए आवश्यक गैस।

"Plants release oxygen during photosynthesis."

carbon dioxide

Meaning: A gas formed when we breathe out or things burn.

अर्थ: कार्बन डाइऑक्साइड – श्वसन व दहन से बनने वाली गैस।

"Lime water turns milky in carbon dioxide."

adulteration

Meaning: Adding cheaper or harmful substances to a product.

अर्थ: मिलावट – किसी उत्पाद में सस्ता/हानिकारक पदार्थ मिलाना।

"Adulteration in food is unsafe."

deteriorate

Meaning: To become worse in quality.

अर्थ: गुणवत्ता का घटना/खराब होना।

"Adulteration can deteriorate the quality of milk."

hazardous

Meaning: Dangerous or harmful.

अर्थ: खतरनाक/हानिकारक।

"Some gases in polluted air are hazardous."

pollutant

Meaning: A substance that makes air, water, or soil dirty or unsafe.

अर्थ: प्रदूषक – हवा/पानी/मिट्टी को गंदा या असुरक्षित करने वाला पदार्थ।

"Smoke is a major air pollutant."

particulate matter

Meaning: Tiny solid or liquid particles suspended in air.

अर्थ: कणिकीय पदार्थ – हवा में तैरते बहुत छोटे ठोस/द्रव कण।

"High particulate matter reduces visibility."

pure substance

Meaning: Matter made of only one kind of particle.

अर्थ: शुद्ध पदार्थ – केवल एक प्रकार के कणों से बना द्रव्य।

"Distilled water is a pure substance."

element

Meaning: A pure substance made of only one kind of atom.

अर्थ: तत्व – केवल एक प्रकार के परमाणु से बना शुद्ध पदार्थ।

"Gold is an element."

compound

Meaning: A pure substance made when elements combine in fixed ratios.

अर्थ: यौगिक – तत्वों के निश्चित अनुपात में मिलकर बना शुद्ध पदार्थ।

"Water is a compound of hydrogen and oxygen."

molecule

Meaning: Two or more atoms bonded together as a unit.

अर्थ: अणु – दो या अधिक परमाणुओं का बंधित समूह।

"An oxygen molecule has two oxygen atoms."

metalloid

Meaning: An element with properties between metals and non‑metals.

अर्थ: उपधातु – जिसकी विशेषताएँ धातु और अधातु के बीच हों।

"Silicon is a metalloid."

ratio

Meaning: A comparison of two quantities by division.

अर्थ: अनुपात – दो मात्राओं की भागफल के रूप में तुलना।

"Water has hydrogen and oxygen in a 2:1 ratio."

decompose

Meaning: To break down into simpler substances.

अर्थ: अपघटित होना – सरल पदार्थों में टूट जाना।

"Sugar can decompose on strong heating."

charcoal

Meaning: A black form of carbon left after burning without air.

अर्थ: कोयला/चारकोल – बिना हवा के जलाने पर बचा काला कार्बन।

"We observed charcoal after heating sugar."

electrolysis

Meaning: Using electricity to split a compound into its parts.

अर्थ: विद्युत अपघटन – बिजली से यौगिक को उसके अवयवों में विभाजित करना।

"Electrolysis of water gives hydrogen and oxygen."

electrode

Meaning: A conductor through which electricity enters or leaves a solution.

अर्थ: इलेक्ट्रोड – वह चालक जिससे विलयन में विद्युत प्रविष्ट/निर्गम होती है।

"Gas bubbles formed at each electrode."

terminal

Meaning: An end or connection point of a battery or device.

अर्थ: टर्मिनल – बैटरी/उपकरण का जोड़ बिंदु।

"Connect the wire to the positive terminal."

hydrochloric acid

Meaning: A strong acid commonly used in laboratories.

अर्थ: हाइड्रोक्लोरिक अम्ल – प्रयोगशालाओं में प्रयुक्त एक प्रबल अम्ल।

"Handle hydrochloric acid with care."

hydrogen

Meaning: A light gas that burns with a pop sound.

अर्थ: हाइड्रोजन – हल्की गैस जो ‘पॉप’ ध्वनि के साथ जलती है।

"Hydrogen gas was collected during electrolysis."

insoluble

Meaning: Not able to dissolve in a particular liquid.

अर्थ: अघुलनशील – किसी द्रव में न घुलने वाला।

"Sand is insoluble in water."

calcium carbonate

Meaning: A white solid formed when CO₂ reacts with lime water.

अर्थ: कैल्शियम कार्बोनेट – CO₂ के चूना जल से अभिक्रिया करने पर बनने वाला श्वेत ठोस।

"Calcium carbonate makes lime water milky."

lime water

Meaning: A clear solution of calcium hydroxide in water.

अर्थ: चूना जल – पानी में कैल्शियम हाइड्रॉक्साइड का स्वच्छ विलयन।

"Blowing into lime water turns it milky."

vigorous

Meaning: Strong, energetic, or forceful.

अर्थ: तेज़/प्रबल – बलपूर्वक या ऊर्जावान।

"Calcium oxide reacts vigorously with water."

native mineral

Meaning: A mineral that is a pure element found in nature.

अर्थ: मौलिक खनिज – प्रकृति में शुद्ध तत्व के रूप में पाया जाने वाला खनिज।

"Gold can occur as a native mineral."

quartz

Meaning: A hard mineral made of silicon dioxide.

अर्थ: क्वार्ट्ज – सिलिकॉन डाइऑक्साइड से बना कठोर खनिज।

"Quartz is used in glass making."

calcite

Meaning: A mineral made of calcium carbonate.

अर्थ: कैल्साइट – कैल्शियम कार्बोनेट से बना खनिज।

"Cement contains calcite."

mica

Meaning: A shiny mineral that splits into thin sheets.

अर्थ: अभ्रक/मीका – चमकीला खनिज जो पतली परतों में टूटता है।

"Mica sheets are used as insulators."

talc

Meaning: A very soft mineral used in talcum powder.

अर्थ: टैल्क – बहुत मुलायम खनिज, टैल्कम पाउडर में प्रयोग।

"Talc is ground to make talcum powder."

graphene aerogel

Meaning: An ultra‑light, porous material made from carbon.

अर्थ: ग्राफीन एरोजेल – कार्बन से बना अति‑हल्का, छिद्रयुक्त पदार्थ।

"Graphene aerogel can soak up oil spills."

porous

Meaning: Full of tiny holes that allow air or liquid to pass.

अर्थ: छिद्रयुक्त – जिसमें सूक्ष्म छिद्र हों।

"Pumice is a porous rock."

absorb

Meaning: To take in liquid or gas.

अर्थ: अवशोषित करना – द्रव या गैस को अपने भीतर लेना।

"Sponge can absorb a lot of water."

NCERT Solutions Class 8 Science - Curiosity Chapter 8 – Nature of Matter: Elements, Compounds, and Mixtures

Chapter Introduction

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Important Points

Practice MCQ Questions (41 questions)

Q1. When two or more substances are mixed and each retains its own properties, it is called:

Q2. A mixture in which all components are evenly distributed and cannot be distinguished is called:

Q3. Elements are pure substances that:

Q4. A compound is formed when:

Q5. What are the two elements that make up water?

Q6. Which of the following is an example of an alloy?

Q7. Lime water turns milky when exposed to air because air contains:

Q8. When sugar is heated, it turns black because:

Q9. Minerals are:

Q10. What is the total number of elements known at present?

Q11. What is the difference between a mixture and a compound?

Q12. In Activity 8.3 (passing electricity through water), hydrogen and oxygen were collected in different volumes. Why was hydrogen collected in a larger volume than oxygen?

Q13. How can you identify hydrogen gas from Activity 8.3?

Q14. In Activity 8.5, Sample A (iron + sulfur mixture) is attracted by a magnet but Sample B (iron sulfide compound) is not. What does this demonstrate?

Q15. Hydrogen sulfide gas from iron sulfide reacting with hydrochloric acid smells like rotten eggs, while hydrogen gas from the same acid reacting with iron is odourless. What does this prove?

Q16. Why cannot the constituent elements of a compound be separated by physical methods?

Q17. Air is a mixture, not a compound. Which fact from the chapter best supports this?

Q18. What is the purpose of separating mixtures in science?

Q19. Why does the chapter classify milk as impure from a scientific standpoint?

Q20. What makes silicon and boron different from typical metals and non-metals?

Q21. In Activity 8.5, iron and sulfur are mixed in a 5.6g:3.2g ratio before heating. Why is this specific ratio used?

Q22. A student heats a mixture of iron and sulfur and forms a black compound. They then test both with a magnet and HCl. What combination of tests conclusively proves a compound was formed?

Q23. Graphene aerogel is described as the lightest material made from carbon. It is highly porous. Why can it absorb oil spills efficiently?

Q24. Cement is made from calcite, quartz, alumina, and iron oxide. These are minerals. What does this tell us about the relationship between minerals, compounds, and practical materials?

Q25. The chapter explains that when sugar heats, carbon and water are produced. This shows sugar is a compound of which elements?

Q26. Two elements—sodium (a reactive metal) and chlorine (a toxic gas)—combine to form sodium chloride (common salt), which is harmless and edible. What general principle does this illustrate about compounds?

Q27. Bromine is one of only two elements that are liquid at room temperature. What is the other?

Q28. The Dhokra art technique uses beeswax to model a shape, covers it in clay, melts the wax, and fills the cavity with molten brass. Which scientific concepts are demonstrated in this process?

Q29. Which of the following are examples of alloys (uniform mixtures of metals)? (Select all that apply)

Q30. Which of the following correctly distinguish a compound from a mixture? (Select all that apply)

Q31. Which of the following are properties of elements as described in the chapter? (Select all that apply)

Q32. A student argues that mixing iron filings and sulfur (Sample A) is the same as making iron sulfide (Sample B) since both are black. Why is this argument flawed?

Q33. A chemist uses solvents to extract compounds from medicinal plants (like Asima Chatterjee did). What does this tell us about the relationship between mixtures, compounds, and science?

Q34. Manufacturing a mobile phone uses more than 45 elements including lithium, cobalt, gold, and silicon. What scientific implication does this have for sustainability?

Q35. In science, a pure substance has only one type of particle, but in common usage 'pure' means unadulterated. How does this distinction matter in analysing food safety?

Q36. Carbon exists as diamond and graphite, both pure carbon but with very different properties. Which of the following BEST explains why these are still called elements and not compounds?

Q37. Which of the following are ways that elements, compounds, and mixtures are used in everyday life as described in the chapter? (Select all that apply)

Q38. Which of the following correctly describe tests to distinguish Sample A (iron+sulfur mixture) from Sample B (iron sulfide compound) in Activity 8.5? (Select all that apply)

Q39. Which of the following correctly describe types of pure substances? (Select all that apply)

Q40. Which of the following correctly describe properties of minerals as described in the chapter? (Select all that apply)

Q41. Which of the following correctly show how understanding elements, compounds, and mixtures has practical applications? (Select all that apply)