Chemistry

This is a multiple choice answer as classified in NCERT Exemplar

(ii) Low atmospheric pressure

Explanation:  The atmospheric pressure drops at high altitude, reducing the solubility of oxygen in blood and tissues.

This is a multiple choice answer as classified in NCERT Exemplar

(iii) Pressure

Explanation:  Because solids and liquids are nearly incompressible, the solubility of a solid in a liquid is unaffected by pressure.

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(ii) Supersaturated

Explanation:  At a certain temperature, a supersaturated solution contains less than the maximum quantity of solute per given amount of solvent. When a small amount of solute is added to a solution like this, it precipitates/crystallizes quickly. A supersaturated solution varies from an unsaturated solution in that it does not precipitate or crystallise when a tiny amount of solute is added to it; instead, it goes into solution and remains dissolved at a specific temperature.

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(iii) Equal to the rate of crystallisation

Explanation : This occurs under equilibrium conditions, i.e. rate of forward reaction (dissolution) = rate of backward reaction (crystallisation).

This is a Multiple choice Questions as classified in NCERT Exemplar

Option (iii)

i.e., Decrease in the amount of dissolved oxygen in water is the answer since organic waste is oxidized by microorganisms in the presence of dissolved oxygen. Hence, oxygen decreases in water as a result it is harmful for aquatic life. 

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(iv) Powdered sugar in hot water.

Explanation: (i) The solubility of a solute/sugar particle increases as its surface area increases. Powdered sugar dissolves more quickly due to its increased surface area.

(ii) Because it provides a cool sensation when touched, sugar dissolving is an endothermic process. Increasing the temperature or using hot water, according to LeChatelier's theory, facilitates sugar breakdown.

This is a Multiple choice Questions as classified in NCERT Exemplar

Option (i) i.e., rich in dissolved oxygen is the answer since the total amount of oxygen consumed by microorganisms in decomposing organic matter present in a certain volume of water is known as Biochemical Oxygen Demand (BOD) of water. If the BOD value is less than 5 ppm, then the sample of water is considered to be pure and is rich in dissolved oxygen. 

This is a Multiple choice Questions as classified in NCERT Exemplar

Option (i)

i.e., Its main components are produced by the action of sunlight on emissions of automobiles and factories is the answer since classical smog is a mixture of smoke, fog and sulphur dioxide and occurs in cold humid climates. While the gases released by automobiles and factories are not responsible for classical fog. 

This is a Multiple choice Questions as classified in NCERT Exemplar

Option (iii)

SO₂ is correct since photochemical fog is formed in the presence of sunlight in summers when NO and hydrocarbons are present in large amounts in the atmosphere. SO₂ is not responsible for photochemical fog.