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The correct answer is (b) A metal

Correct option is D) Acids are formed

(a) (i) Iron (ii) Gold

(b) More heat is evolved during the reaction of sodium metal with water due to which the hyd rogen gas formed catches fire. O n the other hand, less heat is evolved during the reaction of calcium metal with water which cannot make the hydrogen gas bu rn .

Correct option is A) a and b only

(a)M etal oxides are basic in nature and turn red litmus blue. For example: Magnesium oxide. Non-metal oxides are acidic or neutral in nature. The acidic oxides turn blue litmus red. For example: Carbon dioxide.

(b) (i) Acidic oxide: S, C

(ii) Basic oxide: Na, K

(iii) Neutral oxide: H

For rusting, the presence of both oxygen and water (or water vapour) is required. The coat of the paint prevents direct contact of iron with air and oxygen and thus prevents it from rusting.

(a) physical change that can be reversed. 

a) Aluminium has high malleability. So it is very easy to make aluminium foil compared other metals.

b) Because metals are good conductors of electricity. 

c) Iron has more reactivity than copper. So copper cannot displace Iron from its salt solution. 

d) Sodium and potassium have high reactivity with water and an even they burn in the presence of air and water. So these metals are stored in Kerosene.

Malleability is the property of metals to be hammered into thin sheets. Ductility is the property to enable metals to be drawn into wires.

Correct option is A) Malleability

It does not readily react with food items. So aluminium foils are used for wraping food items.

Correct option is C) Gold

Sodium and potassium metals react violently with cold water.

Observations:

1. Metal starts moving over the surface of water making a hissing sound.

2. Metal starts reacting with water causing little explosions.

3. Soon the metal catches fire and starts burning.

Correct option is C) Early tools

Correct option is C) Both ‘A’ and ‘B’

Answer is --- (a) Iron

(a) Metals are malleable i.e. they can be beaten into thin sheets with a hammer.

Example: Aluminium.

Metals are ductile i.e. they can be drawn into thin wires.

Example: Copper.

(b) Aluminium and copper.

(c) Malleability.

(d) Ductility.

(i) Gold and silver are most malleable metal and most ductile metal.

(ii) Silver is the best conductor of heat and lead is the  poorest conductor of heat.

(iii) Metal with highest melting point - Tungsten, iron. Metal with lowest melting point - Gallium, Cesium.

Correct option is A) Silver

1. Malleable: Some metals can be beaten into thin sheets. This property is called Malleability.

2. Ductility: The ability of metals to be drown into thin wires is called ductility.

Correct option is A) Aluminium and copper

Correct option is A) iron and copper

(d) It has not rusted after such a long period

The special quality of the iron pillar at Qutub Minar is that the pillar is not rusted or rather the pillar is rust resistant which depicts the high-quality craftsmanship of Indian craftsman.

1. b. FALSE

2. a. Freely

3. b. FALSE

4. b. Rigid state

Correct option is A) Gold

(b) Both A and R are true but R is not the correct explanation Of A.’

i. a, b and c are correct

(a) Both A and R are true and R is the correct explanation of A.

1. a. Delhi

2. b. NO

3. c. 8m

4. b. Galvanization

5. b. Fe₂O₃ . n₂H₂O

Change in the shape of balloon is done by blowing air into it. This is a man made change. When we left off the air from it, it returns to its normal shape. This is a physical change and reversible one.

(b) Both A and R are true but R is not the correct explanation of A.

1. a. Bad conductors

2. b. Copper

3. b. Alloy

4. b. FALSE

5. b. Bronze

Correct option is  D) above all

1. By keeping the cut vegetables in cold water, we can prevent browning of them. 

2. Cold water prevents the outer surface of the potato and brinjal from colouring. 

3. Small quantities of acids like vinegar or lemon juice in water will also prevent browning of vegetables. 

4. We can also rub the surface of cut fruits with juices of citrus fruits like lemon to avoid from browning. 

5. Ascorbic acid can also be used to prevent browning.

Yes prevent the browning of cut vegetables and fruits.

• Browning of cut apple is due to the oxidation of polyphenols at a particular pH to quinones, which further undergoes polymerization to form brown coloured tannins.
• This browning reaction can be prolonged or slowed down by using reducing agents or by changing the pH.
• Applying lemon juice (i.e., citric acid) on the cut apple, lowers the pH at the surface of the apple. This prevents the oxidation reaction. Thus, browning of cut apple can be prolonged by applying lemon juice.

The correct option is D) none.

a) No physical changes is observed. 

b) The energy is released in the form of heat sound and light energy. 

c) When a piece of wood is burnt a new material is formed (ash). We also notice change in shape and size of new materials (powder). This type of change which leads to form new substance is called chemical changes. 

d) Wood turns into carbon dioxide and ash 

Carbon (Wood) + Oxygen (Air) → CO₂ + Ash

1. Take a small quantity of Camphor in a dish and place it in the open air. 

2. Observe it after some time. Its quantity reduces and we sense the smell of it. 

3. It happens because the camphor gets evaporated. Since it has strong smell, it is used to keep insects and flies away. It is also used in medicines.

1. a. YES

2. b. It becomes Hard and strong

3. a. Mixture of nickel and chromium with iron

4. a. Iron

5. a. TRUE

The correct option is D) above all.

1. Initially Camphor changes into liquid and then evaporates into air. 

2. It is also considered to be a chemical change.

The correct option is C) A & C.

Redox reactions: The reactions in which both reduction and oxidation occur simultaneously are called redox reactions in short.

1. Some articles made up of iron, don’t get rusted even they are exposed to air. 

2. To prevent iron articles from coming into contact with oxygen in air or water or both, we deposit a layer of a metal like Chromium or Zinc on them. 

3. This process of depositing a layer of zinc or Chromium on Iron is called Galvanisation. 

4. Generally we use Zinc for such type of coatings. 

5. We find in our house that water pipe lines are without rust on them. 

6. If we observe carefully, we notice that there is some metallic coating on these pipes to prevent rusting. 

7. They do not get rusted even after a long time since they are galvanized. 

8. The process of depositing one metal on another metal is called galvanisation.

Correct option is A) Iron

Correct option is B) Zinc
 

Galvanizing: Iron or steel that has been coated with a layer of zinc to protect it from corrosion.

(a) Aluminium does not corrode right through because aluminium is more reactive than iron and it forms a layer of aluminium oxide as soon as it comes in contact with moist air. This aluminium oxide layer is very tough and prevents the aluminium underneath from corroding.

(b) The process of thickening of aluminium oxide layer on the surface of aluminium objects by electrolysis is called anodizing. It is done to provide more protection to the aluminium object from corrosion.