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Working principle: 2 Marks
Example: 1 Mark
Distillation is a method used to separate two miscible liquids. When two liquids are miscible and the difference between their boiling point is high, then we use this method.
It is used to separate acetone and water. The boiling point of acetone is 56${}^{\circ }$C, while that of water is 100${}^{\circ }$C.
So, when we heat the mixture of acetone and water above 56${}^{\circ }$C and below 100${}^{\circ }$C, acetone gets evaporated and water remains.
In this way, the mixture of acetone and water gets separated.

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Physical and chemical change: [0.5 Marks each]
1) Photosynthesis and burning of coal $\to$Chemical change.
2) Dissolving sugar in water and melting of wax $\to$Physical change.

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Definition: 1 Mark each.
1) The process of deposition of a layer of zinc on iron is called galvanization. It prevents direct contact of iron with air and oxygen.
2) The process of formation of solid crystals from a homogeneous solution is called crystallization and it is a physical change. Eg: Formation of copper sulphate crystals.

Answer: Option A. -> True
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A
Formation of manure from leaves is a chemical change as a new substance (manure) is formed. The product (manure) has different properties than the original substance (leaves) and this process cannot be reversed.

Answer: Option A. -> A chemical change is irreversible whereas a physical change is reversible.
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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, no new substance is formed whereas, in a chemical change, a new substance is formed. 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. The physical change is temporary and can be reversed while the chemical change is permanent and cannot be reversed.
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.

Answer: Option A. -> CO2(g)+Ca(OH)2(aq)→CaCO3(s)+H2O(l)​
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A
When carbon dioxide is passed through limewater, calcium carbonate is formed.Thismakes the limewater turn milky. The reaction is as follows:
${\text{CO}}_2\text{(g)}+{\text{Ca(OH)}}_2\text{(aq)}\to {\text{CaCO}}_3\text{(s)}+{\text{H}}_2\text{O}\text{(l)}$​

Answer: Option C. -> It involves changes in chemical composition.
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C
Turning milk into curd is a chemical change. A chemical change is defined as a change in which composition of substancechanges. The compositions of curd and milk are different. After converting milk into curd, we cannot get back the milk again. So, it is anirreversible change.

Answer: Option B. -> Burning of wood
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B
The burning of wood is not a physical change because new substances like carbon dioxide and water vapour are formed along with heat and light.In the other cases like cutting of wood, breaking of glass and melting of gold, no new substance is formed. Hence, these are the physical changes.

Answer: Option A. -> True
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A
Food is chemically digested by enzymes. Once food has been broken down, the nutrients are sent into the bloodstream. Food undergoes many chemical changes before being absorbed by the body. Hence, digestion of food is a chemical change as the complex substances that we eat is changed into simpler substances.

Answer: Option B. -> NaHCO3
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B
NaHCO₃ is the chemical formula of Baking soda.