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Each point: [1 Mark]
(a) Lemon juice and vinegar taste sour because they contain acids.
(b)When an acidic solution is mixed with a basic solution, they neutralizeeach other forming salt and water.
(c)Phenolphthalein gives pinkcolour with lime water.

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Each point: 1 Mark
(a)False. Substances can be neutral as well.
(b) False. Acids do not turn all indicators red.
(c)True.Lime water turns red litmus blue because it is basic.
(d) False. It does not change the colour of litmus at all.
(e)False. It is a man-made indicator.

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Explanation: 1 Mark
Components: 1 Mark
Damages: 1 Mark
As the name indicates the rain containing excess of acids is called acid rain.
The rain becomes acidic because carbon dioxide, sulphur dioxide and nitrogen dioxide (which are released into the air as pollutants) dissolve in raindrops to form carbonic acid, sulphuric acid, and nitric acid respectively.
Acid rainis harmful because it can cause damage to buildings, historical monuments, plants, and animals. One of the best examples of harmful effects of acid rains is its effect on Taj Mahal. Taj Mahal is made of marbles which are basic(calcium carbonate). Its colour has changed because of acid rain.

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Name of the substance: 1 Mark
Mechanism: 1 Mark
Examples: 1 Mark
For testing whether a substance is an acid or base, we use indicators.
Indicators are special substances that show a change of colour or smell when added to a solution containing an acidic or a basic substance.
Examples of indicators are: Turmeric, litmus, China rose petals, vanilla, etc.

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Application: 1 Mark
Explanation: 2 Marks
The bacteria present in our mouth produce acid which tends to decay our tooth.
The basic compounds present in our toothpaste neutralize the acids produced by the bacteria and preventthe decay of our tooth.
Hence our toothpaste is basic in nature so that we can prevent tooth decay

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Identification: 1 Mark
Example:1 Mark
The substances that taste bitter and are soapy when rubbed are called bases. Hence this substance isa base.
Sodium hydroxide is an example of a base.

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Litmus paper: 1 Mark
Explanation: 1 Mark
Litmus paper is an indicator. It is used to check whether a solution is acidic or basic.
When treated with a solution containing NaOH, the color of red litmus paper will change to blue as NaOH is a base and bases turn red litmus blue.

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Name of acid: 1 Mark
Cause: 1 Mark
Remedy: 1 Mark
Hydrochloric acid is an acid in our stomach which helps in digestion.
Too much of acid in the stomach causes acidity. To relieve acidity, we take an antacid such as milk of magnesia, which contains magnesium hydroxide.
It neutralises the effect of excessive acid as it is basic in nature.

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Source: 1 Mark
Colour: 1 Mark
Litmus is extracted from lichens.
When added to an acidic solution, it turns red and when added to a basic solution, it turns blue.
It has mauve (purple) colour in distilled water which is neutral.

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Each correct match: 1 Mark
(a) (iii)Tartaric acid is present in unripe mangoes.
(b) (v)Calcium hydroxide is present in lime water.
(c) (iv)Formic acid is present in ant's sting.
(d) (i) Sodium hydroxide is present in soap.
(e) (ii)Lactic acid is present in curd.