CG Board Class 8 Science Chapter 5 Solutions: Metals and Non-metals (धातु और अधातु) – 2026-27

Fill in the blanks: The number of metals is ____________ than non-metals.

more

Fill in the blanks: ____________ is a good conductor of heat and electricity.

Copper (or Iron)

Fill in the blanks: ____________ is fragile or brittle.

Coal (or Sulphur / Graphite)

Fill in the blanks: ____________, ____________ and ____________ are examples of metals.

Iron, Copper and Aluminium

Choose the correct alternative: Metals are (harder/softer) than non-metals.

harder

Choose the correct alternative: Most of the metals are (bad/good) conductors of heat.

good

Choose the correct alternative: (Metals/Non-metals) have lustre.

Metals

Choose the correct alternative: The property of metals to be beaten into thin sheets is called (ductility/malleability).

malleability

What is the nature of the हल of magnesium oxide dissolved in water?

The हल of magnesium oxide in water is basic (alkaline) in nature. It turns red litmus paper blue.

Balanced Chemical Equation:

MgO + H_2O → Mg(OH)₂

(Magnesium oxide + Water → Magnesium hydroxide)

What happens when zinc pieces are put into copper sulphate हल?

Zinc is more reactive than copper. When zinc pieces are added to a blue copper sulphate हल, zinc displaces copper from the हल, forming a colourless zinc sulphate हल and depositing a reddish-brown layer of copper metal.

Balanced Chemical Equation:

Zn (s) + CuSO₄ (aq) → ZnSO₄ (aq) + Cu (s)

(Zinc + Copper sulphate → Zinc sulphate + Copper)

Does copper displace iron from ferrous sulphate हल?

No, copper cannot displace iron from ferrous sulphate हल because copper is less reactive than iron in the metal reactivity series.

Why are pickles not kept in aluminium or iron vessels?

Pickles contain organic acids (such as acetic acid or citric acid). Acids react with metals like aluminium and iron to form poisonous metallic salts and release hydrogen gas. Eating these contaminated food items can cause food poisoning and health hazards. Therefore, acidic pickles are stored in glass or ceramic containers.

Which gas is produced normally when metals react with acids?

Hydrogen gas (H₂) is liberated when metals react with dilute acids. It burns with a characteristic pop sound when a burning matchstick is brought near it.

Example Reaction:

Zn + 2HCl → ZnCl₂ + H₂↑

What are noble metals?

Metals that are extremely unreactive and do not react with air, water, moisture, acids, or alkalis under normal conditions are called noble metals. Examples include Gold (Au), Silver (Ag), and Platinum (Pt).

What do you understand by corrosion? How can you protect metals from corrosion by electroplating?

• Corrosion: The slow destruction and degradation of metal surfaces due to chemical reactions with atmospheric gases, moisture, and acids is called corrosion (e.g., rusting of iron).
• Protection by Electroplating: Electroplating is a process of depositing a thin, uniform protective layer of a non-corrosive metal (such as chromium, nickel, or tin) onto the surface of an iron or steel object using electric current. This protective metallic layer prevents direct contact of the underlying base metal with moist air, thereby preventing corrosion.

Give the constituents of bronze and steel.

For what is chlorine and tincture iodine used?

1. Chlorine (Cl₂): Used as a disinfectant to purify drinking water and kill harmful germs.
2. Tincture Iodine: A हल of iodine in alcohol and water, used as an antiseptic medicine on wounds and cuts to prevent infection.

This is not a property of metals:

(a) Fragility

(b) Conduction of electricity

(c) High density

(d) Malleability and ductility

(a) Fragility / (a) भँगुरता

Out of the three pins of gold, silver and iron which pin can get a coat of copper when dipped in copper sulphate हल:

(a) Iron

(b) Gold

(c) Silver

(d) None of these

(a) Iron / (a) लोहा

Which halogen is used as an antiseptic?

(a) Fluorine

(b) Chlorine

(c) Bromine

(d) Iodine

(d) Iodine / (d) आयोडीन

Iron rusts:

(a) Only in air

(b) Only in presence of carbon dioxide

(c) Only in water

(d) In presence of both air and water

(d) In presence of both air and water / (d) हवा और पानी दोनों की उपस्थिति में

An example of Noble metal is:

(a) Iron

(b) Copper

(c) Gold

(d) Aluminium

(c) Gold / (c) सोना

Which of these is classified as metal or non-metal:

(a) Element

(b) Compound

(c) Mixture

(d) All of these

(a) Element / (a) तत्व

1. English: All metals are solid at room temperature.

Evaluation: False (Mercury is a liquid metal at room temperature).

Hindi: सभी धातुएँ कमरे के ताप पर ठोस होती हैं। (असत्य – पारा कमरे के ताप पर द्रव धातु है)।

1. English: Sodium is more reactive than magnesium.

Evaluation: True.

Hindi: सोडियम, मैग्नीशियम की तुलना में अधिक क्रियाशील है। (सत्य)।

1. English: Stainless steel is an alloy of iron, nickel, carbon and chromium.

Evaluation: True.

Hindi: स्टेनलेस स्टील लोहा, निकेल, कार्बन और क्रोमियम की मिश्रधातु है। (सत्य)।

1. English: Non-metals react with oxygen to form alkaline oxides (basic oxide).

Evaluation: False (Non-metals form acidic oxides).

Hindi: अधातुएँ ऑक्सीजन से अभिक्रिया करके क्षारीय ऑक्साइड बनाती हैं। (असत्य – अधातुएँ अम्लीय ऑक्साइड बनाती हैं)।

1. English: Rusting is an example of corrosion of metals.

Evaluation: True.

Hindi: जंग लगना धातुओं के संक्षारण का एक उदाहरण है। (सत्य)।

Differentiate metals and non-metals on the basis of physical and chemical properties. Write three differences of each.

Why are gold and silver used for making ornaments?

Gold and silver are used for making ornaments due to the following reasons:

1. Noble Nature: They are noble metals that do not react with air, water, moisture, or household chemicals, maintaining their shiny appearance for a long time without rusting or tarnishing.
2. High Lustre: They possess attractive metallic lustre and reflection.
3. High Malleability and Ductility: They can easily be beaten into extremely thin sheets and drawn into fine wires, allowing artisans to craft intricate jewelry designs.

What do you understand by reactivity series?

The reactivity series is an arrangement of metals in descending order of their chemical reactivity. Metals positioned at the top (e.g., Sodium, Potassium) are most reactive, while metals at the bottom (e.g., Gold, Platinum) are least reactive. A more reactive metal displaces a less reactive metal from its salt हल.

Reactivity Order:

Li > K > Na > Ca > Mg > Al > Zn > Fe > Pb > H > Cu > Hg > Ag > Au

How much carat is pure gold? Why is pure gold not used for making ornaments?

Pure gold is 24 carats (100% pure gold).

Pure gold is extremely soft and malleable. Ornaments made from pure 24-carat gold can bend, deform, or break easily under mild force. To increase its hardness and mechanical strength, a small amount of copper or silver is alloyed with it (e.g., 22-carat gold contains 22 parts pure gold and 2 parts copper/silver).

What are alloys? Give names of any four alloys and write their constituents and uses.

An alloy is a homogeneous mixture of two or more metals, or a metal and a non-metal, blended together in molten state to achieve superior properties like hardness, strength, and corrosion resistance.

Table of Four Alloys:

What is metal corrosion? What are the ways to protect corrosion?

• Metal Corrosion: The gradual wearing away and destruction of a metal surface due to chemical reaction with oxygen, moisture, and acids present in air is called metal corrosion (e.g., rusting of iron).
• Ways to Protect Metals from Corrosion:

1. Painting: Applying a layer of paint blocks direct contact with moist air (e.g., iron gates, vehicles).
2. Greasing / Oiling: Applying grease on moving machinery parts prevents moisture exposure.
3. Galvanization (Zinc Coating): Coating iron objects with molten zinc metal prevents rusting.
4. Electroplating: Depositing a protective layer of tin or chromium using electricity.
5. Alloying: Converting iron into stainless steel resists corrosion.

Why is graphite used as an electrode?

Graphite is a non-metal, but owing to its unique crystalline structure with free electrons, it is an exceptionally good conductor of electricity. Additionally, it has a high melting point and is chemically inert (unreactive). Therefore, graphite rods are used as durable electrodes in electric dry cells and electrolysis processes.

Why is pure iron not used in making railway tracks?

Pure iron is relatively soft, flexible, and rusts very rapidly when exposed to rain and moist atmospheric air. Trains carrying heavy loads exert immense pressure, which would cause pure iron tracks to bend, deform, or break, leading to severe train accidents. Instead, Steel (an alloy of iron and carbon) or manganese steel is used because it is extremely hard, strong, and highly resistant to wear, pressure, and rust.

Explain through an activity that Magnesium is more reactive than Iron.

Activity / Experiment:

1. Take two test tubes and label them A and B.
2. In Test Tube A, take 10 mL of light green Ferrous Sulphate हल (FeSO₄) and place a clean piece of Magnesium ribbon in it.
3. In Test Tube B, take 10 mL of colourless Magnesium Sulphate हल (MgSO₄) and place a clean iron nail in it.
4. Leave both test tubes undisturbed for 30 minutes.

Observation:

• Test Tube A: The light green colour of Ferrous Sulphate हल fades away and turns colourless, while a reddish-grey deposit of displaced iron metal forms over the magnesium ribbon.
• Test Tube B: No change occurs.

Chemical Equation:

Mg (s) + FeSO₄ (aq) → MgSO₄ (aq) + Fe (s)

Conclusion: Magnesium displaces iron from its salt हल, proving that Magnesium is more reactive than Iron (Mg > Fe).

Rub any copper vessel with sand paper and observe. Now explain giving reasons.

Observation: When a dull green-coated copper vessel is rubbed with sandpaper, the green surface layer gets scraped away, revealing a shining reddish-brown surface underneath.

Explanation and Reason:

When copper vessels are exposed to moist air containing carbon dioxide and oxygen over time, copper undergoes slow atmospheric corrosion to form a thin green dull coating of basic copper carbonate on its surface.

Corrosion Reaction:

2Cu + H_2O + CO₂ + O₂ → CuCO₃ · Cu(OH)_{2Basic Copper Carbonate (Green Layer)}

Rugging the vessel with abrasive sandpaper physically removes this corroded green coating, exposing the clean, highly reflective reddish-brown pure copper metal below.