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Which of the following mixtures would you be able to separate using the method of filtration? (a) Oil in water (b) Cornflakes in milk (c) Salt in water (d) Sugar in milk

Answer: (b) Cornflakes in milk Since cornflakes are insoluble in milk it can be separated by the method of filtration. The majority of times, the... View Article

Boojho’s grandmother is suffering from diabetes. Her doctor advised her to take ‘Lassi’ with less fat content. Which of the following methods would be most appropriate for Boojho to prepare it? (a) Filtration (b) Decantation (c) Churning (d) Winnowing

Answer: (c) Churning Butter (fat) is separated by churning the curd and the remaining lassi contains less fat content. The majority of times, the... View Article

Paheli bought some vegetables such as French beans, lady’s finger, green chillies, brinjals and potatoes all mixed in a bag. Which of the following methods of separation would be most appropriate for her to separate them? (a) Winnowing (b) Sieving (c) Threshing (d) Hand-picking

Answer: (d) Hand-picking Since the vegetables are big in size handpicking is the best method for separating the vegetables. The majority of... View Article

lt was Paheli’s birthday, her brother Simba was helping her to decorate the house for the birthday party and their parents were also busy making other arrangements. Following were the activities going on at Paheli’s home: (i) Simba blew balloons and put them on the wall. (ii) Some of the balloons got burst. (iii) Paheli cut colourful strips of paper and put them on the wall with the help of tape. (iv) She also made some flowers by origami (paper folding) to decorate the house. (v) Her father made dough balls. (vi) Mother rolled the dough balls to make puries. (vii) Mother heated oil in a pan. (viii) Father fried the puries in hot oil. Identify the activities at Paheli’s home as those that can be reversed and those which cannot be reversed.

Answer: Activities which are reversible: (i) Simba blew balloons and put them on the wall. (iv) She also made some flowers by origami (paper... View Article

Paheli mixed flour and water and (i) made dough, (ii) rolled the dough to make chapati, (iii) baked the chapati on a pan, (iv) dried the chapati and ground it in a grinder to make powder. Identify the changes (i) to (iv) as the changes that can be reversed or that cannot be reversed.

Answer: (i) Making of dough from flour and water is an irreversible change. (ii) Rolling the dough to make a chapati is a reversible change.... View Article

Change of a bud into a flower is a change which cannot be reversed. Give four more such examples.

Answer: Examples of changes which cannot be reversed are listed below. Digestion of food Ripening of fruits Burning of wood Milk into curd... View Article

Conversion of ice into water and water into ice is an example of change which can be reversed. Give four more examples where you can say that the changes can be reversed.

Answer: Examples of changes which can be reversed are listed below. (i) Folding of a paper (ii) Melting of wax (iii) Knitting of a sweater (iv)... View Article

A potter working on his wheel-shaped a lump of clay into a pot. He then baked the pot in an oven. Do these two acts lead to the same kind of changes or different? Give your opinion and justify your answer.

Answer: (a) The shaping of clay into a pot is just a physical change in the clay's shape. This change is reversible.(b) The chemical... View Article

Give one example in each case: (a) Change which occurs on heating but can be reversed. (b) Change which occurs on heating but cannot be reversed. (c) Change which occurs on cooling but can be reversed. (d) Change which occurs on mixing two substances, but can be reversed. (e) Change which occurs on mixing two substances, but cannot be reversed.

Answer: Here are examples for the above statements: (a) Heating of an iron rod (b) Baking of chapati (f) Formation of ice from water (d)... View Article

Tearing of paper is said to be a change that cannot be reversed. What about paper recycling?

Answer: Recycling of paper is also classified as an irreversible change because the quality, colour and texture of the paper change on recycling... View Article

Boojho’s sister broke a white dove, a symbol of peace, made of Plaster of Paris (POP). Boojho tried to reconstruct the toy by making a powder of the broken pieces and then making a paste by mixing water. Will he be successful in his effort? Justify your answer.

Answer: No, he will not achieve in his effort. When a toy is produced with plaster of Paris(POP), the POP hardens due to the development of new... View Article

Which of the following changes cannot be reversed? (a) Blowing of a balloon (b) Folding a paper to make a toy aeroplane (c) Rolling a ball of dough to make roti (d) Baking cake in an oven (e) Drying a wet cloth (f) Making biogas from cow dung (g) Burning of a candle

Answer: The following changes cannot be reversed: (d) Baking a cake is irreversible. (f) Making biogas from cow dung is irreversible. (g) Burning... View Article

Can we reverse the following changes? If yes, suggest the name of the method. (a) Water into water vapour (b) Water vapour into water (c) Ice into water (d) Curd into milk.

Answer: (a) Water into water vapour – Yes, by using the method of condensation, water vapour can be converted to water. (b) Water vapour... View Article

Paheli had bought a new bottle of pickle from the market. She tried to open the metal cap to taste it but could not do so. She then took a bowl of hot water and immersed the upper end of the bottle in it for five minutes. She could easily open the bottle now. Can you give the reason for this?

Answer: When exposed to heat, almost all metals expand. As a result, when the jar is immersed in hot water, the metal cap expands and opens easily.... View Article

A piece of iron is heated until it becomes red-hot. It then becomes soft and is beaten to the desired shape. What kinds of changes are observed in this process-reversible or irreversible?

Answer: It is a reversible change when a piece of iron on heating can be beaten into the desired shape. Since the object of the desired shape... View Article

Look at figure which shows three situations (a) a burning candle (b) an extinguished candle (c) melting wax. Which of these shows a reversible change and why?

Answer: Melting of wax in figure (c) is a reversible change because the melted wax can be solidified again. Any changes which can be reversed... View Article

The iron rim is made slightly smaller than the wooden wheel. The rim is usually heated before fixing into the wooden wheel because on heating the iron rim (a) expands and fits onto the wooden wheel (b) contracts and fits onto the wooden wheel (c) no change in the size takes place (d) expands first, then on cooling contracts and fits onto the wooden wheel.

Answer: (d) expands first, then on cooling contracts and fits onto the wooden wheel. Iron expands on heating. So the smaller iron rim expands on... View Article

Rolling of chapati and baking of chapati are the changes that (a) can be reversed (b) cannot be reversed (c) can be reversed and cannot be reversed, respectively (d) cannot be reversed and can be reversed, respectively

Answer: (c) can be reversed and cannot be reversed, respectively Once the chapati is baked it cannot be reversed. But rolling of chapati is a... View Article

Salt can be separated from its solution (salt dissolved in water), because (a) mixing of salt in water is a change that can be reversed by heating and melting of salt (b) mixing of salt in water is a change that cannot be reversed (c) mixing of salt in water is a permanent change (d) mixing of salt in water is a change that can be reversed by evaporation

Answer: (d) mixing of salt in water is a change that can be reversed by evaporation Salt can be separated from water solution by evaporating the... View Article

While lighting a candle, Paheli observed the following changes. (i) Wax was melting (ii) Candle was burning (iii) Size of the candle was reducing (iv) Melted wax was getting solidified Of the above, the changes that can be reversed are (a) (i) and (ii) (b) (ii) and (iii) (c) (iii) and (iv) (d) (i) and (iv)

Answer: (d) (i) and (iv) Wax was melting; Melted wax was getting solidified. Solid wax can be melted and melted wax gets solidifies again. Hence... View Article

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