Nature of Matter: Elements, Compounds, and Mixtures — Mastery

Q1. From the chapter opener, which of the following is NOT an example of matter?

• A. A wooden staircase
• B. The water in a bottle
• C. A book in a school bag
• D. A thought in Sumana's mind

Q2. Why does the chapter open the topic of mixtures with poha and sprout salad rather than chemical examples?

• A. Because both are pure substances
• B. Because both are elements with fixed compositions
• C. Because both turn lime water milky
• D. Because both are familiar foods built by mixing several ingredients without chemical reactions

Q3. From everyday examples, which row contains ONLY non-uniform mixtures?

• A. Sand and water, muddy water, oil and water
• B. Air, seawater, brass
• C. Vinegar, sugar solution, bronze
• D. Stainless steel, brass, bronze

Q4. A teacher dissolves sugar fully in a glass of water and asks students whether they can see the sugar. The best chapter-grounded reply is

• A. No, because sugar has chemically reacted with water
• B. Yes, because all mixtures show their components clearly
• C. Yes, if a magnifying glass is used
• D. No, because the components are evenly distributed and indistinguishable even with a microscope

Q5. Stainless steel, the alloy used for everyday utensils, is a uniform mixture of

• A. Copper and zinc
• B. Copper and tin
• C. Iron, nickel, chromium and a small amount of carbon
• D. Aluminium and silver

Q6. In Activity 8.1, calcium oxide (quick lime) is added slowly to water. The product formed in this first step is

• A. Calcium carbonate
• B. Calcium chloride
• C. Calcium sulfate
• D. Calcium hydroxide

Q7. In Activity 8.2 (a black sheet of paper kept near an open window for a few hours), tiny particles settle on the paper. The chapter classifies these particles as

• A. An integral part of air
• B. Components of a uniform mixture only
• C. Water droplets from the air
• D. Pollutants suspended in air

Q8. From Table 8.1, vinegar (acetic acid in water) and oil-and-water are both 'liquid and liquid' mixtures. The correct uniform/non-uniform tags for them are

• A. Vinegar — uniform; Oil and water — non-uniform
• B. Vinegar — non-uniform; Oil and water — uniform
• C. Both uniform
• D. Both non-uniform

Q9. The chapter describes adulteration as an illegal process. Which best captures the chapter's reason for calling it harmful?

• A. It changes the colour of milk and ghee
• B. It always makes the product cheaper than it should be
• C. It can deteriorate quality and make the product hazardous to health
• D. It converts every product into a mixture from a pure substance

Q10. The 'Safety first' note for Activity 8.3 specifies the use of a 9 V battery but explicitly bans the use of a lithium-ion battery. The most reasonable safety reason is

• A. Li-ion batteries are too expensive for school use
• B. Li-ion batteries can be unsafe when used in liquids or in the presence of acids
• C. Li-ion batteries do not produce hydrogen
• D. Li-ion batteries always melt their electrodes

Q11. Atoms of most elements cannot exist independently. When two atoms of hydrogen combine, they form one stable particle of hydrogen called a

• A. Compound of hydrogen
• B. Mixture of hydrogen
• C. Molecule of hydrogen
• D. Crystal of hydrogen

Q12. Although they are solid elements at ordinary room temperature, gallium and caesium turn into liquids near a temperature of about

• A. 30 °C (303 K)
• B. 100 °C (373 K)
• C. 0 °C (273 K)
• D. 1000 °C (1273 K)

Q13. Common salt dissolved in water can be separated from water by evaporation. Can the salt itself be split into sodium and chlorine in the same way?

• A. Yes, evaporation will separate sodium from chlorine
• B. Yes, simple filtering will do it
• C. No, because the constituents of a compound cannot be separated by any physical method
• D. No, because sodium chloride is a uniform mixture, not a compound

Q14. Sodium chloride (common salt) is made of particles of sodium and chlorine in the ratio

• A. 1 : 1
• B. 1 : 2
• C. 2 : 1
• D. 3 : 1

Q15. In Activity 8.5, the chapter specifies that the iron filings and sulfur powder taken on a watch glass weigh

• A. 3.2 g iron and 5.6 g sulfur
• B. 5 g iron and 5 g sulfur
• C. 1.0 g iron and 1.0 g sulfur
• D. 5.6 g iron and 3.2 g sulfur

Q16. The chapter gives the word equation for the reaction of iron in Sample A with dilute hydrochloric acid as

• A. Iron + Dilute Hydrochloric acid → Iron oxide + Water
• B. Iron + Dilute Hydrochloric acid → Iron sulfate + Sulfur dioxide
• C. Iron + Dilute Hydrochloric acid → Iron chloride + Hydrogen gas
• D. Iron + Dilute Hydrochloric acid → Iron carbonate + Carbon dioxide

Q17. The chapter equation for the reaction of Sample B with dilute hydrochloric acid is

• A. Iron sulfide + Dilute Hydrochloric acid → Iron chloride + Hydrogen sulfide
• B. Iron sulfide + Dilute Hydrochloric acid → Iron oxide + Sulfur
• C. Iron sulfide + Water → Iron hydroxide + Sulfur
• D. Iron sulfide + Dilute Hydrochloric acid → Iron + Sulfur + Hydrogen

Q18. Which 'wonder' material developed by material scientists is made from carbon and said to be the lightest material on earth?

• A. Graphene aerogel
• B. Stainless steel
• C. Talcum powder
• D. Cement

Q19. According to the chapter, cement is made from minerals or things obtained from minerals such as

• A. Quartz only
• B. Talc and mica
• C. Pyroxene and olivine
• D. Calcite, quartz, alumina and iron oxide

Q20. In the Dhokra art process described in the chapter, the wax model is covered with clay and heated. The wax then

• A. Melts out, leaving a hollow space that is filled with molten brass or bronze
• B. Hardens permanently into the design
• C. Reacts chemically with clay to form bronze
• D. Becomes the final golden surface of the figure

Q21. Exercise Q11 asks for two compounds made only from non-metals. Which pair fits and matches the chapter's everyday examples?

• A. Sodium chloride (table salt) and iron oxide (rust)
• B. Magnesium oxide (in fireworks) and iron sulfide
• C. Water (for drinking) and carbon dioxide (used by plants in photosynthesis)
• D. Aluminium oxide (sandpaper) and calcium carbonate (chalk)

Q22. Exercise Q12 asks: how can gold be classified as both a mineral and a metal? The correct reasoning is

• A. Gold is a compound of two elements and only a mineral
• B. Gold is only a metal; calling it a mineral is wrong
• C. Gold is a mixture of silver and copper
• D. Gold is a native mineral (a pure element found naturally) and is also classified as a metal because of its metallic properties

Q23. A Class 8 teacher in Rampur wants students to fill Table 8.3 with carbon dioxide, sand, seawater, magnesium oxide, sodium chloride and aluminium. The correct row for the 'Mixtures' column is

• A. Aluminium and magnesium oxide
• B. Carbon dioxide and sodium chloride
• C. Sand and seawater
• D. Magnesium oxide and sodium chloride

Q24. Asha, a Class 8 student, thinks Sample B (iron sulfide) is still a mixture because 'it was made from iron and sulfur, just heated'. Which response best addresses her misconception?

• A. Tell her she is right because Sample B contains iron atoms inside it.
• B. Ask her to weigh Sample B; if it weighs the same as the original mixture, it is still a mixture.
• C. Tell her every black powder is a compound.
• D. Ask her to bring a magnet near Sample B; since no iron is attracted, the iron is now chemically locked inside a new compound.

Q25. A teacher wants to demonstrate the presence of carbon dioxide in the air to her Class 8 students. Which of the following is the MOST effective demonstration grounded in this chapter?

• A. Leave a petri dish of lime water near an open window for a few hours and have students observe the milkiness.
• B. Show students a chemical formula on the blackboard and ask them to memorise it.
• C. Burn a candle in front of the class and explain that the smoke shows CO₂.
• D. Ask students to inhale and exhale deeply and 'feel' the carbon dioxide in the air.

Q26. Exercise Q9 asks: how would our daily lives be changed if water were a mixture of hydrogen and oxygen instead of a compound? Which response best evaluates the change, using the chapter's logic?

• A. There would be no change because water would still look the same.
• B. Water would still extinguish fire, because mixtures behave like compounds.
• C. Plants would stop growing, because they need only compounds, not mixtures.
• D. Drinking water could catch fire from a spark, since hydrogen (fuel) and oxygen (combustion-supporter) would not be chemically locked together.

Q27. The 'A step further' box lists major air pollutants. Which set is given by the chapter?

• A. Particulate matter (dust, soot), carbon monoxide, ozone, nitrogen dioxide and sulfur dioxide
• B. Nitrogen, oxygen, argon, water vapour and carbon dioxide
• C. Hydrogen sulfide, methane, ammonia and chlorine
• D. Only carbon dioxide and water vapour

Q28. From the chapter's element list, which set contains ONLY metals?

• A. Carbon, sulfur, hydrogen, oxygen
• B. Silicon, boron, mercury, bromine
• C. Helium, neon, argon, krypton
• D. Gold, silver, magnesium, iron, aluminium

Q29. The chapter says the manufacturing of a mobile phone — its screen, battery and other components — uses more than how many different elements?

• A. About 10 elements
• B. About 20 elements
• C. About 80 elements
• D. About 45 elements

Q30. Why does the chapter argue that understanding how elements combine to form compounds is the 'key to innovation' and not just academic recognition?

• A. Because chemists can make new colours for paintings.
• B. Because it allows scientists to discover new elements.
• C. Because it lets people memorise the periodic table faster.
• D. Because understanding element-combinations lets chemists invent life-saving medicines and vaccines, and create fertilisers that increase crop production for a growing human population.