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Melting of wax is a change where a solid changes to a liquid state. Give one more such change which you observe in your surroundings.

Answer: Physical change – The type of change in which the physical properties of a material change. It can be... View Article

State whether the given statements is true or false: Stretching of the rubber band is not a physical change.

Answer: Stretching of the rubber band is not a physical change – False Stretching of the rubber band is a... View Article

State whether the given statements is true or false: Ships suffer a lot of damage though they are painted.

Answer: Ships suffer a lot of damage though they are painted- True Physical change The type of change in which... View Article

State whether the given statements is true or false: Anaerobic bacteria digest animal waste and produce biogas.

Answer: Anaerobic bacteria digest animal waste and produce biogas – True Physical change The type of change in which the... View Article

State whether the given statements is true or false: When a candle burns, both physical and chemical changes take place.

Answer: When a candle burns, both physical and chemical changes take place – True Physical change The type of change... View Article

Two drops of dilute sulphuric acid were added to 1 g of copper sulphate powder and a then a small amount of hot water was added to dissolve it (step I). On cooling, beautiful blue coloured crystals got separated (step II). Step I and Step II are: (a) physical and chemical changes, respectively. (b) chemical and physical changes, respectively. (c) both physical change. (d) both chemical change.

Answer: (c) both physical changes. Dissolution of copper sulphate powder in water in the presence of sulphuric acid is a... View Article

Which of the following statement is incorrect for a chemical reaction? (a) Heat may be given out but never absorbed. (b) The sound may be produced. (c) A colour change may take place. (d) A gas may be evolved.

Answer: (a) Heat may be given out but never absorbed. A chemical reaction is in which the bonds are broken... View Article

Paheli’s mother made a concentrated sugar syrup by dissolving sugar in hot water. On cooling, crystals of sugar got separated. This indicates a – (a) a physical change that can be reversed. (b) the chemical change that can be reversed. (c) a physical change that cannot be reversed. (d) the chemical change that cannot be reversed.

Answer: (a) a physical change that can be reversed. A chemical change results from a chemical reaction, while a physical... View Article

Galvanisation is a process used to prevent the rusting of which of the following? (a) Iron (b) Zinc (c) Aluminium (d) Copper

Answer: (a) Iron Galvanizing is a process in which iron or steel is coated with a thin layer of zinc... View Article

Iron pillar near the Qutub Minar in Delhi is famous for the following facts. Which of these facts is responsible for its long stability? (a) It is more than 7 metres high. (b) It weighs about 6000 kg. (c) It was built more than 1600 years ago. (d) It has not rusted after such a long period.

Answer: (d) It has not rusted after such a long period. Other metals are mixed into iron, resulting in a... View Article

A man painted his main gate made up of iron, to i) prevent it from rusting. ii) protect it from the sun. iii) make it look beautiful. iv) make it dust-free. Which of the above statement(s) is/are correct? (a) (i) and (ii) (b) (ii) and (iii) (c) only (ii) (d) (i) and (iii)

Answer: (d) (i) and (iii) Iron is unaffected by sunlight. As a result, there’s no need to cover it from... View Article

Which of the following is/are true when milk changes into curd? i) Its state is changed from liquid to semi-solid. ii) It changes colour. iii) It changes the taste. iv) The change cannot be reversed. Choose the correct option from below : (a) (i) and (ii) are correct (b) (ii) and (iii) are correct (c) (i), (iii) and (iv) are correct (d) (i) to (iv) are correct

Answer: (c) (i), (iii) and (iv) are correct When milk turn to curd it changes its shape to semisolid, its... View Article

A chemical change may involve – (a) change in colour only (b) change in temperature only (c) evolution of gas only (d) any or all of the above

Answer: (d) any or all of the above A chemical change results from a chemical reaction. If the chemical composition... View Article

Which of the following is a chemical change? (a) Twinkling of stars (b) Cooking of vegetables (c) Cutting of fruits (d) Boiling of water

Answer: (b) Cooking of vegetables A chemical change results from a chemical reaction. Physical change is when matter changes forms... View Article

Which of the following is a physical change? (a) Rusting of iron (b) Combustion of magnesium ribbon (c) Burning of candle (d) Melting of wax

Answer: (d) Melting of wax A chemical change results from a chemical reaction, while a physical change is when matter... View Article

Explain two neutralisation reactions related to a daily life situation.

Answer: A neutralization reaction can be defined as a chemical reaction in which an acid and base quantitatively react together... View Article

Paheli observed that most of the fish in the pond of her village were gradually dying. She also observed that the waste of a factory in their village is flowing into the pond which probably caused the fish to die. (a) Explain why the fish were dying. (b) If the factory waste is acidic in nature, how can it be neutralised?

Answer: (a) Factory wastes may have a large proportion of basic or acidic substances. These pollutants make it harder to... View Article

You are provided with three test tubes A, B and C as shown in Figure with different liquids. What will you observe when you put (a) a piece of blue litmus paper in each test tube. (b) a piece of red litmus paper in each test tube. (c) a few drops of phenolphthalein solution to each test tube.

Answer: Test tube Effect on blue litmus Effect on red litmus Effect on Phenolphthalein Solution A Turns red Remains red... View Article

You are provided with four test tubes containing sugar solution, baking soda solution, tamarind solution, salt solution. Write down activity to find nature (acidic/basic/neutral) of each solution.

Answer: Add blue litmus solution and then red litmus solution for the test tubes containing sugar solution, baking soda solution,... View Article

A farmer was unhappy because of his low crop yield. He discussed the problem with an agricultural scientist and realised that the soil of his field was either too acidic or too basic. What remedy would you suggest the farmer to neutralise the soil?

Answer: Bases such as quick lime (calcium oxide) or slaked lime (calcium hydroxide) are used to treat soils that are... View Article

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