Answer: Option A. -> In a physical change, no new substance is formed whereas in a chemical change, a new substance is formed.
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A
A change can be physical or chemical, depending on whether or not it involves the formation of a new substance.
In a physical change, the product formed has the same properties as the original substance whereas, in a chemical change, the product formed has different properties than the original substance. Some of the examples of physical changes are melting of ice, cutting a fruit,etc. Some of the examples of chemical changes are burning of wood, rusting of iron, etc.

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Changes in which new substances are formed are called chemical changes.
Chemical changesoccur when a substance combines with another to form a new substance, called synthesisor, alternatively, decomposesinto two or more different substances.At the molecular level, chemical change involves making orbreakingof bonds between atoms.

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Explanation: 2 Marks
Figure: 1 Mark
(i) Take a separating funnel. After setting up the separating funnel, pour the kerosene oil and water mixture in it.
(ii) Let it stand undisturbed for some time. Soon two distinct and separate layers of oil and water will be seen.
(iii) Next, open the stopcock of this separating funnel. The aim is to drain out the water slowly which has collected at the base of the funnel.

(iv) Close the stopcock of this separating funnel as soon as the level of oil reaches the stopcock.

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Each part: 1.5 Marks
(a) When candle burns, both physical and chemical changes take place. On burning, the candlewax melts but can be solidified again on cooling. This shows that melting of wax is a physical change.
The burning of candle also produces light and carbon dioxide. Hence, it is also a chemical change.
(b)A reversible change is a type of change in which a substance that is undergoing a change can be recovered in its original form. An irreversible change is a type of change in which a substance cannot be reobtained inits original form. In the cooking of rice, raw rice cannot be obtained from cooked rice. Therefore, this change is an irreversible change.

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Each step: 1 Mark
Following are the steps for the formation of copper sulphate crystals:
(i) Take a cupful of water in a beaker and add a few drops of sulphuric acid into it.
(ii)Heat the water and add copper sulphate powder slowly into it.
(iii) Continue adding copper sulphate powder till no more copper sulphate can be dissolved.
(iv) Filter the solution and allow it to cool.
(v) After some time, when the solution has cooled down,clear crystals of copper sulphatewill be visible.

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Changes in which only physical properties of a substance change are called physical changes. In a physical change, no new substance is formed.
For example cutting of wood is a physical change or conversion of water into vapours.

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Each point: 1 Mark
1) Evaporation is the process of loss of water as water vapour from the surface of water.
2) Evaporation is a physical change. When the water vapour is allowed to be cooled, its physical state changes back to liquid form.

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Reason: 3 Marks
Rotten food smellsbad because of the chemical reactions occurring in it due to the action of microorganisms. Rotting alters the composition of the substance, the old bonds of the reactants are broken down and fresh bonds are formed, resulting in the formation of new products with different properties.

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Definition: 1 Mark
Factors: 2 Marks
Preventive measures: 2 Marks
Rust is a reddish- or yellowish-brown coating of iron oxide that is formed on iron or steel by oxidation, especially in the presence of moisture.
The presence of water and oxygen is essential for the rusting of iron. However, Impurities in the iron, the presence of water vapor, acids, salts and carbon dioxide hasten rusting. Again,pure iron does not rust in dry and carbon dioxide free air. It also does not rust in pure water, free from dissolved salts.
$Iron\left(Fe\right)+Oxygen(O_2,fromtheair)+water\left(H_{2}O\right)\to Rust\left(ironoxide\right)(F{e}_2{O}_3.H_{2}O)$
The various measures that can be taken to prevent rusting of Iron are:
i) Galvanisation: It is the process of deposition of a layer of zinc on iron. It prevents rusting of iron.
ii) We can apply a coat of paint or grease on iron.

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(a) Explanation: 2 Marks
(b) Explanation: 1 Mark
(a) Whenbaking soda is added to lemon juice, a chemical change occurs. In this reaction, a new substance is formed which is carbon dioxide along with the evolution of heat.It is a chemical changeand thereactionisirreversible.
The equation for the reaction is as follows:
Sodium Bicarbonate + Citric acid $\to$ Sodium Citrate + Carbon dioxide + Water + Heat
(b)Food is chemically digested by enzymes. Once food has been broken down, the nutrients are sent into the bloodstream where they find their way into the liver. Food undergoes manychemical changes before being absorbed by the body. Hence digestion of food is a chemical changeasthe complex substances that we eat ischanged intosimpler substances (new products).