CBSE Class 8 Science Chapter 4 / materials metals and non-metals / Most important Question

Q1. Which of the following represents a displacement reaction?

  1. X → Y + Z  
  2. A + B → C 
  3. A + BC  → AC + B    
  4. PQ + RS → PS + RQ 

Solution

Those reactions in which one element takes the place of another element in a compound are known as displacement reactions. In reaction, A + BC → AC + B A takes the place of element B in its compound BC to form product AC.

Q2. Which of the following is TRUE about metals?

  1. They are good conductors of heat.
  2. They are good insulators of electricity.
  3. They cannot be hit and hammered into shape.
  4. They are always brittle.

Solution

Metals allow heat to pass through them. Therefore, they are good conductors of heat.

Q3. From the given three equations, which metal will be the most reactive out of the given metals? Zn + PbSO4  ZnSO4 + PbFe + CuSO4  FeSO4 + CuFe + ZnSO4  FeSO4 + Zn

  1. Fe
  2. Cu
  3. Zn
  4. Pb

Solution

In 1st equation Zn displaces Pb. But in 2nd and 3rd chemical equations, Fe displaces both Cu and Zn. So, Fe is the most reactive.

Q4. We use aluminum foils for wrapping food. This shows that aluminium is:

  • 1) Malleable
  • 2) Strong
  • 3) Sonorous
  • 4) Ductile

Solution

Metals can be beaten to thin sheets. This property is known as malleability.

Q5. Considering the following reactions, which is the most reactive metal of the given metals?Mg + ZnSO4 → MgSO4 +Zn2Na + MgSO4 → Na2SO4 + Mg2Na + ZnSO4  → Na2SO4 +Zn

  • 1) S
  • 2) Na
  • 3) Zn
  • 4) Mg

Solution

This is since both Na and Mg are displacing zinc from zinc sulphate Solution, so both are more reactive than zinc. But Na is displacing Mg from its salt Solution. Hence, Na is more reactive than Mg.

Q6. How do you know that a substance is a metal?

  • 1) It conducts heat.
  • 2) Both A and B.
  • 3) It conducts electricity.
  • 4) It is brittle.

Solution

Metals are substances that are good conductors of heat and electricity.

Q7. Which gas is evolved when carbon reacts with dilute sulphuric acid?

  • 1) CO2
  • 2) Carbon does not react with dilute sulphuric acid.
  • 3) SO2
  • 4) H2

Solution

Carbon is non-metal and non-metals do not react with acids.

Q8. When sulfur dioxide dissolves in water, it produces:

  • 1) sulfur
  • 2) sulphuric acid
  • 3) sulphurous acid
  • 4) sulphur trioxide

Solution

Non-metal oxide on reaction with water produces acidic Solution.

Q9. Which of the following metal is present in blood?

  • 1) Magnesium
  • 2) Iron
  • 3) Potassium
  • 4) Hydrogen

Solution

Iron is the metal present in blood hemoglobin.

Q10. What happens when zinc is added to a Solution of iron sulphate?

  • 1) Green precipitate will be formed.
  • 2) Green Solution is obtained; no precipitate is formed.
  • 3) Grey precipitate will be formed.
  • 4) Zinc will not displace iron from its Solution.

Solution

Zinc is more reactive than iron. Therefore, when zinc is added to the Solution of iron sulphate, the colour of iron sulphate Solution changes and a grey precipitate of iron and a colourless Solution of zinc sulphate is formed.

Q11. The property that allows metals to be hit and hammered into thin sheets is:

  • 1) Sonorous
  • 2) Ductility
  • 3) Brittle
  • 4) Malleability

Solution

The property that allows metals to be hit and hammered into thin sheets is malleability.

Q12. The metal which is used in constructing railway lines and girders is:

  • 1) Iron
  • 2) Copper
  • 3) Zinc
  • 4) Aluminium

Solution

Iron is used in constructing railway lines and girders because it is a very strong metal.

Q13. Tungsten is used in electric bulbs because of its:

  1. Conductivity
  2. Sonority
  3. Ductility
  4. Malleability

Solution

Tungsten is used in electric bulbs because it is metallic in nature and hence conducts electricity.

Q14. (i) Name the metal which is used for decorating sweets and which property makes it suitable for this?

(ii) Write another use of this metal.

Solution

(i) Silver foils are used for decorating sweets. It is because of its high malleability, silver metal can be hammered into thin silver sheets.

(ii) Silver metal is used for making jewelry.

Q15. Select the correct pair of metals that cannot be stored in air.

  1. Calcium and Magnesium
  2. Potassium and Sodium
  3. Calcium and Iron
  4. Sodium and Magnesium

Solution

Both sodium and Potassium are very reactive metals. They catch fire when exposed to air, therefore are stored in kerosene.

Q16. Sodium metal is kept immersed in kerosene and not water because:

  1. It reacts violently with oxygen and water.
  2. It reacts violently with water but not with oxygen.
  3. It reacts with kerosene.
  4. It reacts violently with oxygen but not with water.

Solution

Sodium is a highly reactive metal and reacts violently with oxygen and water producing a large amount of heat and light.

Q17. Which of the following material will heat up fast?

  1. Metal spoon
  2. Plastic spoon
  3. All will get heated equally
  4. Wood spoon

Solution

As metals are good conductors of heat, they will heat up fast.

Q18. Which of the following is the only liquid metal?

  1. Iron
  2. Mercury
  3. Sulphur
  4. Aluminium

Solution

Mercury is the only metal which is liquid at room temperature.

Q19. Which is a property of an acidic oxide?

  1. No effect on litmus papers.
  2. Turns moist red litmus paper blue.
  3. Turns both litmus paper to yellow.
  4. Turns moist blue litmus paper red.

Solution

Acidic oxides turns moist blue litmus paper to red being acidic in nature.

Q20. Which of the following is used in cookware?

  1. Metal
  2. Any available material
  3. Non-metal
  4. Metalloid

Solution

Cookwares are made of metals as they are good conductors of heat.

Q21. Rust of iron is basically:

  • 1) A chloride
  • 2) A nitride
  • 3) A sulphide
  • 4) An oxide

Solution

Iron reacts with water and oxygen to produce rust which is an oxide. The reaction is as follows: 4Fe + 3O2 + 2H2O → 2Fe2O3.2H2O Iron rusts in moist air to form hydrated ferric oxide.  

Q22. Select the pair that shows similar type of reaction with air and water.

  • 1) S and Cu
  • 2) Mg and N
  • 3) C and Ca
  • 4) Cu and Ca

Solution

Both Copper (Cu) and Calcium (Ca) are metals. They react with air and water to produce a compound that is basic in nature.

Q23. What happens when a piece of copper metal is placed in an iron sulfate?

  • 1) Green colour Solution of iron sulphate changes to blue Solution of copper sulphate.
  • 2) Deep blue colour Solution of iron sulphate changes to green Solution of copper sulphate.
  • 3) Grey precipitate of iron is formed.
  • 4) Copper will not displace iron from its Solution.

Solution

When a piece of copper is placed in iron sulphate Solution then no change will be observed. This is because copper is less reactive than iron, therefore, unable to displace it from its Solution.

Q24. Which of the following metal doesn’t react with water as well as with steam?

  • 1) Magnesium
  • 2) Zinc
  • 3) Lead
  • 4) Iron

Solution

Lead does not react with water (or even steam).

Q25. (i)CuSO4 + Fe → FeSO4 + Cu

(ii)FeSO4 + Zn → ZnSO4 + Fe Which of the following statement is true on the basis of above reactions?

  • 1) Iron is the most reactive out of zinc, copper and iron.
  • 2) Copper is the most reactive metal out of zinc,copper and iron.
  • 3) Zinc is the most reactive metal out of zinc, copper and iron.
  • 4) Iron is the least reactive metal out of zinc, copper and iron.

Solution

In the first reaction, Fe displaces Cu. Therefore, Fe is more reactive than Cu (reactivity of Fe > reactivity of Cu). In the second reaction Fe is displaced by Zn. Therefore, Fe is less reactive than Zn (reactivity of Zn > reactivity of Fe). Therefore, Zn is more reactive and Cu is least reactive.

Q26. (i) Give name of two metals which are used for making frying pans and geysers. Which property makes them suitable for making utensils and water boilers?

(ii) Name a metal which is a poor conductor of heat.

Solution

(i) Copper and aluminium are used for making frying pans and geysers because they are very good conductors of heat.

(ii) Lead is a poor conductor of heat.

Q27. _______ gas burns with a pop sound.

Solution

Hydrogen gas burns with a pop sound.

Q28. Which of the following reaction will not occur?

  1. CuSO4 + Fe → FeSO4 + Cu
  2. FeSO4 + Zn → ZnSO4 + Fe
  3. Cu + AgNO3  → CuNO3+ Ag
  4. ZnSO4+ Cu →  CuSO4+ Zn

Solution

Copper is less reactive than zinc so it cannot displace zinc from its Solution. Therefore, this reaction will not occur.

Q29. The substances calcium, copper and aluminum, all are _______.

Solution

The substances calcium, copper and aluminum, all are metals.

Q30. The metal which reacts with water only when it is red hot is:

  • 1) Copper
  • 2) Calcium
  • 3) Iron
  • 4) Sodium

Solution

Iron reacts with water only when it is red hot and steam is passed over it. 3Fe + 4H2O(steam) https://images.topperlearning.com/topper/questions/192170_image1_0.png Fe3O4 + 4H2

Q31. The property that allows heat and electricity to pass through metals easily is:

  • 1) Insulation
  • 2) Density
  • 3) Lustre
  • 4) Conduction

Solution

Metals are good conductors of heat and electricity as they allow it to pass through them.

Q32. Metals are ________ conductors of electricity.

Solution

Metals are good conductors of electricity.

Q33. Gold and silver are most malleable metals.

  • 1) False
  • 2) True

Solution

True

Q34. Hydrochloric acid turns:

  1. Red litmus Solution blue.
  2. No change in colour
  3. Red litmus Solution yellow
  4. Blue litmus Solution red

Solution

Acids turn blue litmus Solution red.

Q35. _______ are used to make strings of musical instruments.

Solution

Metals are used to make strings of musical instruments.

Q36. Sodium catches fire when it comes in contact with water because:

  • 1) The reaction of sodium metal with water is highly heat producing due to which the hydrogen gas formed during the reaction catches fire and burns causing little explosions.
  • 2) The reaction of sodium metal with water is highly heat producing due to which the NaOH formed during the reaction catches fire and burns causing little explosions.
  • 3) The reaction of sodium metal with water is highly heat producing due to which the oxygen gas formed during the reaction catches fire and burns causing little explosions.
  • 4) Sodium is an explosive metal.

Solution

Sodium reacts vigorously with cold water forming sodium hydroxide (NaOH) and hydrogen(H2). The reaction of sodium metal with water is highly heat producing due to which the hydrogen gas formed during the reaction catches fire and burns causing little explosions.

Q37. Aluminium is light in weight and a good conductor of heat.

  • 1) True
  • 2) False

Solution

True

Q38. Name: (a) A metal which is liquid at room temperature.

(b) Two metals that are soft and can be cut with a knife.

Solution

(a) A metal which is liquid at room temperature:- Mercury

(b) Two metals which are soft and can be cut with a knife :- Sodium and potassium

Q39. What products are formed when aluminum reacts with dilute sulphuric acid?

  • 1) Al2O + H2+ SO2
  • 2) Al(OH)3+ H2+ SO2
  • 3) Al2(SO4)3+ 3H2+ SO2
  • 4) Al2(SO4)3+ 3H2

Solution

Aluminum reacts with dilute sulphuric acid to form aluminium sulphate with the liberation of hydrogen gas. 2Al + 3H2SO4 → Al2(SO4)3+ 3H2 ↑

Q40. Differentiate between metals and non-metals on the basis of their physical properties (four points).

Solution

Difference in Physical Properties of Metals and Non-Metals:   Metals Non-metals

1. Metals are malleable and ductile.

1. Non-metals are neither malleable nor ductile.

2. Metals are good conductors of heat and electricity.

2. Non-metals are poor conductors of heat and electricity.(except graphite which is a good conductors of electricity).

3. Metals are lustrous.

3. Non-metals are non-lustrous.

4. Metals are strong.They have high tensile strength.(except sodium and potassium which are not strong and have low tensile strength).

4. Non-metals are not strong.They have low tensile strength.    

Q41. What does this reaction suggest?MgSO4 + Cu  CuSO4 + Mg

  • 1) This reaction can not occur.
  • 2) This reaction is a decomposition reaction.
  • 3) This reaction occurs only at high temperatures.
  • 4) Copper is more reactive than magnesium.

Solution

Metal that are less reactive, cannot displace more reactive metal from their salt Solution. Hence the reaction will not occur.

Q42. (i) Why does copper coin dissolve in the Solution of silver nitrate if it is immersed in it for some time?

(ii) What colour change is observed?

Solution

(i) Copper is more reactive than silver. Therefore, when copper coin is kept immersed in a Solution of silver nitrate, it will displace silver from silver nitrate Solution and a Solution of copper nitrate will be formed. Thus, copper coin will dissolve in the Solution.

(ii) The colour of the Solution will change from colourless to blue.

Q43. Which of the following metals can be easily cut with a knife?

  • 1) Copper
  • 2) Iron
  • 3) Sodium
  • 4) Aluminium

Solution

Sodium is a metal that is very soft and can be easily cut with a knife.

Q44. What products are formed when iron (Fe) reacts with dilute hydrochloric acid (HCl)?

  • 1) FeCl3 + 2H2
  • 2) FeCl + H2
  • 3) FeCl2 + H2
  • 4) FeH2+ Cl2

Solution

Fe + 2HCl  FeCl2 + H2

Q45. Metals are generally good thermal and electrical conductors.

  • 1) False
  • 2) True

Solution

True

Q46. (i) Fe + CuSO4  FeSO4 + Cu

(ii) Zn + FeSO4  ZnSO4 + Fe On the basis of the above reactions, indicate which is most reactive and which is least reactive metal out of zinc, copper, and iron.

Solution

In the first reaction, Fe displaces Cu. Therefore, Fe is more reactive than Cu (reactivity of Fe> reactivity of Cu). In the second reaction, Fe is displaced by Zn. Therefore, Fe is less reactive than Zn (reactivity of Zn> reactivity of Fe). Therefore, Zn is more reactive and Cu is least reactive.

Q47. Coal is malleable.

  • 1) True
  • 2) False

Solution

False. Coal is non-metal hence it does not show the malleability

Q48. Write the equations for the reactions of (i) Iron with dilute hydrochloric acid.

(ii) Aluminium with dilute hydrochloric acid

(iii) Gold with dilute hydrochloric acid

Solution

  • Fe + 2HCl ➜ FeCl2 + H2 
  • (ii) Al + 6HCl ➜ AlCl3 + 3H2 
  • (iii) Au + HCl ➜ no reaction

Q49. A screw-driver is provided with a wooden handle as it is not slippery.

  • 1) False
  • 2) True

Solution

False. A screw-driver is provided with wooden handle as it is slippery.

Q50. Metals are more important to human life than non-metals.

  • 1) False
  • 2) True

Solution

False. Metals, as well as non-metals, are important to human life.

Q51. Why is copper a good metal to use for electrical wires?

  • 1) It is shiny.
  • 2) It is good conductor of electricity.
  • 3) It is cheap.
  • 4) It is easily available.

Solution

Copper is a good conductor of electricity.

Q52. Metals and water react to form a metal _______ and hydrogen gas.

Solution

Metals and water react to form a metal hydroxide and hydrogen gas.

Q53. Metals react with water to form either their respective oxides or hydroxides and liberate:

  • 1) Oxygen gas
  • 2) Carbon dioxide gas
  • 3) Steam
  • 4) Hydrogen gas

Solution

Metals react with water to form either their respective oxides or hydroxides and liberate hydrogen gas.

Q54. Oxide of magnesium is basic in nature because:

  1. When magnesium oxide is dissolved in water then resulting Solution is a base which does not change the colour of red litmus paper.
  2. When magnesium oxide is dissolved in water then resulting Solution is a base which turns blue litmus to red.
  3. When Magnesium oxide is dissolved in water then resulting Solution is a base which turns red litmus to blue.
  4. When magnesium oxide is dissolved in water then resulting Solution has no action on dry red litmus paper.

Solution

Oxide of magnesium is basic in nature because when magnesium oxide is dissolved in water then the resulting Solution is basic in nature due to the presence of Mg(OH)2 which turns red litmus to blue. MgO + H2O https://images.topperlearning.com/topper/questions/192202_image1_0.png Mg(OH)2

Q55. Select a basic oxide.

  • 1) H2O
  • 2) CuO
  • 3) NO
  • 4) P2O5

Solution

Metals on reaction with oxygen produce basic oxides.

Q56. Gold metal is used for making jewellery because it only reacts with air and that too slowly.

  • 1) True
  • 2) False

Solution

True

Q57. The metals which are usually used for making cooking utensils and water boilers are:

  • 1) Aluminium, magnesium
  • 2) Aluminium, Copper
  • 3) Zinc, iron
  • 4) Copper, Zinc

Solution

Copper and aluminium are used for making cooking utensils and water boilers because they are very good conductors of heat.

Q58. All metals react equally with water and air.

  • 1) True
  • 2) False

Solution

False. Some metals react with water and air.

Q59. Carbon dioxide dissolves in water to form _______ acid.

Solution

Carbon dioxide dissolves in water to form carbonic acid.

Q60. Why are metals used for making electric cables?

Solution

Metals are good conductors of electricity and are ductile i.e. can be drawn into thin wires hence they are used for making wires.

Q61. Metals can be easily beaten into sheets, this property is called _______.

Solution

Metals can be easily beaten into sheets, this property is called malleability.

Q62. Non-metals are found as solids, liquids or gases.

  • 1) True
  • 2) False

Solution

True

Q63. The property of metals by which they can be drawn into wires is called ________.

Solution

The property of metals by which they can be drawn into wires is called ductility.

Q64. (i)Explain, why, when a copper object remains in damp air for a considerable time, a green coating is formed on its surface. What is the chemical formula of that green colour substance?

(ii) Write the chemical reaction involved.

Solution

(i) When a copper object remains in damp air for a considerable time, a green coating of copper carbonate is formed on its surface. It is formed due to the reaction of copper with carbon dioxide of air and water vapour also present in air. The chemical formula of green colour substance is CuCO3(copper carbonate). (ii) 2Cu + H2O + CO2 + O2 https://images.topperlearning.com/topper/questions/192611_image002.gif Cu(OH)2 + CuCO3

Q65. A metal with silvery appearance is slowly tarnished in air. It reacts with boiling water and evolves hydrogen gas. Dilute hydrochloric acid reacts vigorously with metal evolving hydrogen gas.

(i)Identify the metal and

(ii) Also write the reactions involved.

Solution

(i)The metal is magnesium.

(ii)Mg + 2H2O  Mg(OH)2 + H2     Mg + 2HCl MgCl2 + H2

Q66. Generally, non-metals are not lustrous. Which of the following non-metal is lustrous?

  • 1) Nitrogen
  • 2) Iodine
  • 3) Oxygen
  • 4) Sulphur

Solution

Generally, non-metals are not lustrous but iodine being an exception is lustrous.

Q67. Which property of metals makes them suitable for use in jewelry?

Solution

Two properties of metals makes them suitable for use in jewellery: (a) Metals have a shiny lustre. (b) Metals are malleable and ductile.

Q68. Metal detectors work on the principle of conduction of electricity by metals.

1) True

2) False

Solution

True

Q69. (i) Why does the colour of copper sulphate Solution change when an iron nail is kept immersed in it? What is the change in color observed?

(ii) What happens to the iron metal?

Solution

(i) Iron metal is more reactive than copper. Therefore, it displaces copper from copper sulphate Solution (CuSO4). The deep blue colour of copper sulphate Solution fades due to the formation of light green Solution of iron sulphate.

(ii) A red-brown coating of copper metal is formed on the surface of iron nail.

Q70. (i) What happens when potassium comes in contact with water? (ii) Write chemical reaction involved.

Solution

(i) Potassium reacts vigorously with cold water forming potassium hydroxide (KOH) and hydrogen (H2). The reaction of potassium metal with water is highly heat producing due to which the hydrogen gas formed during the reaction catches fire immediately. (ii) 2K + 2H2O https://images.topperlearning.com/topper/questions/192650_image002.gif 2KOH + H2 + Heat

Q71. The green coating on copper vessel is a mixture of __________ and copper hydroxide.

Solution

The green coating on copper vessel is a mixture of copper carbonate and copper hydroxide.

Q72. What is meant by saying that metals are:

  • (i) malleable
  • (ii) ductile
  • (iii) lustrous
  • (iv) conductors, and
  • (v) sonorous?

Give one application or use of each property.

Solution

  • Malleable: This means that metals can be beaten into thin sheets with a hammer. The property which allows the metals to be hammered into thin sheets is called malleability. Aluminium metal can be hammered to form alumimium foils. 
  • Ductile: This means that metals can be drawn (or stretched) into thin wires. The property which allows the metals to be drawn into thin wires is called ductility. Copper metal can be drawn into thin copper wires (used as electric wires).
  • Lustrous: This means that metals have a shiny appearance. The shiny appearance of the metals is called metallic lustre. Gold metal is used for making jewellery because of its shiny lustre.
  • Conductors: This means that metals allow heat and electricity to pass through them easily. Copper metal is used in making cooking utensils because of its high heat conductivity. (v) Sonorous: This means that metals make a ringing sound when we strike them. The property by virtue of which metals make a ringing sound is called sonority. Metal sheets are used for making bicycle bells and temple bells.  

Q73. Name a metal which is used in making mirrors. Which property makes it suitable for this?

Solution

Silver metal is used in making mirrors. Due to shiny appearance silver metal is an excellent reflector of light.

Q74. (i) Copper is used for making electric wires. But how do metals conduct electricity? (ii) Which metal is the best conductor of electricity?

Solution

  • Metals offer very less resistance to the flow of electric current. They conduct electricity because of the presence of free electrons in them. These free electrons can move easily through the metal and thus conduct electricity.
  • Silver is the best conductor of electricity.

Q75. Which physical property of metals is shown in following picture of a shining spoon, knife and fork?

Solution

The shining spoon, knife and fork are made of metals. This shows that metals have shiny lustre.

Q76. All metals are solids except __________.

Solution

All metals are solids except mercury.