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Magnesium burns with a dazzling white flame to form magnesium oxide, a powdery mass. The color of magnesium oxide is milk white.

Air is a mixture can be supported by the following evidence.

1. Variable composition at different places

2. Lacks distinct properties of its own

3. Has no definite boiling point

4. Components of air cannot be easily separated by physical means.

5. Formation of air does not involve any energy change.

6. Cannot be represented by a chemical formula.

1. Sulphur dioxide gas can cause acid rain.

2. Every nine parts of water by weight contains eight parts by weight of oxygen.

3. Dust particles help in the precipitation of water vapor in the air.

4. Helium gas is used for filling weather observation balloons.

5. Solution of carbon dioxide in water is called carbonic acid.

When sulphur burns in oxygen, the color of the flame is brilliant blue

(a) We will observe that fine water droplets get deposited on the outer wall of the glass tumbler. 

(b) The candle burn more brightly because candle gets oxygen support in burning. 

(c) When CO₂ gas is passed through lime water it forms calcium carbonate which is white precipitate (turbidity). This gives the milky white appearance to the solution.

4. LPG and CNG

Water vapour present in air, condenses on the cooler surface of the tumbler. Hence they condenses into tiny water droplets.

The active component of air which supports combustion and is used up in burning.

Oxygen.

Carbon dioxide and water vapor are formed due to the burning of the candle.

(a) Aquatic animals and plants use oxygen dissolved in water and survive. 

(b) Oxygen is necessary for combustion when covered with a glass tumbler supply of oxygen stops. 

(c) For artificial respiration mountaineers carry oxygen cylinders as at high altitudes, the air is thin and breathing becomes difficult. Also divers carry oxygen cylinder for artificial respiration as there is less oxygen dissolved in water (less dense) and breathing becomes difficult. 

(d) These bubbles come from the air dissolved in water. The marine life uses air dissolved in water.

Types of soil 

1. Sandy soil 

2. Clayey soil 

3. Loamy soil

The boiling point of water is 100°C.

(b) Freezing point

Components of air arc Nitrogen, Oxygen, Carbon Dioxide and other gases.

Animals and plants take oxygen from the atmosphere and give out carbon dioxide in the atmosphere. During photosynthesis, plants take in carbon dioxide and release oxygen gas. The above mentioned processes occur simultaneously and so, the proportion of oxygen and carbon dioxide gas in the atmosphere remains constant. So plants and animals are interdependent.

Soil is the uppermost part of the earth, which is formed by the mixture of various substances produced by the weathering of rocks and minerals and decomposition of organic matter, due to action of wind, water and climate.

Sugar is completely soluble in water. Oxygen is also soluble in water, due to which aquatic animals perform respiration, so we can say that water is a universal solvent.

(i)—(c), (ii)—(a), (iii)—(b), (iv)—(b), (v)—(b).

(i) Atmosphere is a thin blanket of air that surrounds the earth. It protects us from the harmful rays of
the sun. It consists of several gases in which nitrogen and oxygen occupy the major portion.
(ii) Nirtrogen (78%) and oxygen (21%) make the bulk of the atmosphere.
(iii) Carbon dioxide creates greenhouse effect in the atmosphere.
(iv) Weather is hour-to-hour, day-to-day condition of the atmosphere.
(v)
* Convectional rainfall
* Orographic rainfall
* Cyclonic rainfall.
(vi) The pressure exerted by the weight of air on the earth’s surface is known as air pressure.

Acid rain affects us in many ways. 

Some of the consequences are given below.

1. It irritates eyes and skin of human beings. 

2. It inhibits germination and growth of seedlings. 

3. It changes the fertility of the soil, destroys plants and aquatic life. 

4. It causes corrosion of many buildings, bridges, etc. 

Preventive measures: 

Acid rain and its effects can be controlled by the following ways. 

1. Minimizing the usage of fossil fuel such as petrol, diesel etc. 

2. Using CNG (Compressed Natural Gas). 

3. Using non – conventional source of energy. 

4. Proper disposal of the industrial wastes.

The time taken for the candle to extinguish depends upon the volume of the containers. Lor less volume, the time taken is less. Lor more volume, the time taken is more.

(a) Troposphere

The most abundant element in the earth’s crust Oxygen.

A) Avoid contact with hanging, loose electrical wires

(a) heavier than air

1. Reduction in the use of fossil fuels. 

2. Restricting the use of CFC’s.

1. Using CNG 

2. Proper disposal of the industrial wastes.

1. Melting of ice cap and glaciers.

2. Increase in frequency of floods, soil erosion and un – seasonal rains. 

3. Loss of biodiversity due to the extinction of coral reefs and other key species. 

4. Spreading of waterborne and insect-borne diseases.

Preventive measures: 

• Reduction in the use of fossil fuels. Controlling deforestation. 
• Restricting the use of CFCs. 
• Planting more trees.
• Reducing, reusing and recycling resources.

1. Increase in frequency of floods, soil erosion and unseasonal rains. 

2. Loss of biodiversity due to the extinction of coral reefs and other key species.

Physical properties of carbon dioxide: 

• Carbon dioxide is a colorless and odorless gas. 
• It is heavier than air. 
• It does not support combustion. 
• It is fairly soluble in water and turns blue litmus slightly red. So it is acidic in nature. 
• It can easily be liquefied under high pressure and can also be solidified. This solid form of CO₂ is called dry ice which undergoes sublimation.

Uses of Nitrogen: 

1. Liquid nitrogen is used as a refrigerant. 

2. It provides an inert atmosphere for conducting certain chemical reactions. 

3. It is used to prepare ammonia (by Haber’s process) which is then converted into fertilizers and nitric acid. 

4. It is used for inflating tyres of vehicles. 

5. It is used for filling the space above mercury in high temperature thermometer to reduce the evaporation of mercury. 

6. Many explosives such as TNT (Trinitrotoluene), nitroglycerin and gun powder contain nitrogen. 

7. It is used for the preservation of fresh foods, manufacturing of stainless steel, reducing fire hazards and as part of the gas in incandescent light bulbs.

The increased green house effect is caused due to increase in the air pollutants and it results in the average increase of temperature of the atmosphere. This is called as Global warming.

Aerated water is nothing but carbon dioxide dissolved in water under pressure. This is also called soda water.

(d) Supports burning

(c) carbon dioxide

Physical properties of oxygen:

1. Oxygen is a colorless, odorless and tasteless gas. 

2. It is a poor conductor of heat and electricity 

3. Oxygen dissolves readily in cold water. 

4. It is denser than air. 

5. It can be made into liquid (liquefied) at high pressure and low temperature. 

6. It supports combustion.

Carbon dioxide is present in air to the extent of about 0.03% in volume. It is evolved by the plants and animals during respiration and is produced during fermentation reactions. Much of the naturally occurring CO₂ is emitted from the magma through volcanoes. CO₂ may also originate from the bio – degradation of oil and gases. Human CO₂ emissions upset the natural balance of the carbon cycle.

Physical properties of nitrogen:

1. It is a colorless, tasteless and odorless gas. 

2. It is slightly lighter than air. 

3. It is slightly soluble in water. 

4. Nitrogen becomes a liquid at low temperature and looks like water. When it freezes, it becomes a white solid. 

5. It is neutral to litmus like oxygen.

Ca(OH)₂ + CO₂ → CaCO₃ + H₂O.

1. Carbon dioxide (CO₂) 

2. Sulphur dioxide (SO₂) 

3. Phosphorus trioxide (P₂O₃) (or) Phosphorus pentoxide (P₂O₅) 

4. Magnesium Oxide (MgO) 

5. Iron Oxide (Fe₂O₃) 

6. Sodium Oxide (Na₂O)

(d) sodium carbonate

1. Atmospheric air, water. 

2. Plants and animals. 

3. Minerals in the form of silicates, carbonates, oxides.

(a) blue litmus to red

(b) Nitrogen

1. Oxygen 

2. lighter 

3. Nitrogen 

4. refrigerant 

5. rusting

(c) Carbon dioxide

Carbon dioxide gas is acidic in nature.