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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

An iron ring is heated. Which of the following statement about it is incorrect? (a) The ring expands. (b) The ring almost comes to the same size on cooling. (c) The change, in this case, is reversed. (d) The ring changes its shape and the change cannot be reversed.

Answer: (d) The ring changes its shape and the change cannot be reversed. The change is reversible in case of an iron ring. Since the ring... View Article

Which of the following change cannot be reversed? (a) Hardening of cement (b) Freezing of ice cream (c) Opening a door (d) Melting of chocolate

Answer: (a) Hardening of cement Hardening of cement is cannot be reversed because once hardened it cannot come back to its original shape. Change... View Article

Pick the change that can be reversed from the following. (a) Cutting of trees (b) Melting of ghee (c) Burning of candle (d) Blooming of flower

Answer: (b) Melting of ghee The melted ghee can be frozen again hence this change can be reversed. Change in chemistry can be explained on the... View Article

Sugar, salt, mustard oil, sand, sawdust, honey, chalk powder, petals of a flower, soil, copper sulphate crystals, glucose, wheat flour are some substances given to Paheli. She wants to know whether these substances are soluble in water or not. Help her in identifying soluble and insoluble substances in water.

Answer: The solubility is the maximum amount of solute that can dissolve in a known quantity of solvent at a certain temperature. The... View Article

Differentiate among opaque, translucent and transparent materials, giving one example of each.

Answer: Opaque materials Translucent materials Transparent materials Those substances through which objects cannot be seen are termed... View Article

Why do you think oxygen dissolved in water is important for the survival of aquatic animals and plants?

Answer: Materials that can be compressed are known as soft materials. Materials that cannot be compressed are known as hard materials. Lustrous... View Article

Chalk, iron nail, wood, aluminium, candle, cotton usually look different from each other. Give some properties by which we can prove that these materials are different.

Answer: Few properties by which we can prove that these materials are different: Chalk – Hard, rough, non-lustrous Iron nail –... View Article

Arrange the jumbled words to arrive at the appropriate names of materials and also write two uses of each. (a) milaunuim (b) tcaslpi (c) soekrnee (d) gavnier

Answer: The arranged word are: (a) Aluminium – It can be used to wrap food in the foil, in making aircraft, etc. (b) Plastic – It... View Article

During summer holidays, a group of children collected a lump of salt, green grass, broken glass piece, a small thermocol box, pen, iron nail, glass marbles, hair, naphthalene ball, a piece of sugar candy (mishri) and tried to group them on the basis of properties given in table below. Help them in filling the table.

Answer: Transparent substances are those substances or materials that allow things to be seen through them. Almost all light beams are able to... View Article

You are provided with the following materials – turmeric, honey, mustard oil, water, glucose, rice flour, groundnut oil. Make any three pairs of substances where one substance is soluble in the other and any three pairs of substances where one substance remains insoluble in the other substances.

Answer: In our daily lives, we come into contact with a variety of substances. We experiment with them and come to a few conclusions before... View Article

Which among the following materials would you identify as soft materials and why? Ice, rubber band, leaf, eraser, pencil, pearl, a piece of a wooden board, cooked rice, pulses and fresh chapati.

Answer: Leaf, rubber band, cooked rice, eraser and fresh chapati are soft materials because they can be scratched or compressed easily.... View Article

Take a small cotton ball and place it in a tumbler/ bowl filled with water. Observe it for at least 10 minutes. Will it float or sink in water and why?

Answer: When a cotton ball is placed in water, it floats at first, but as the water is absorbed by the cotton by capillary action and the air... View Article

On a bright sunny day, Shikha was playing hide and seek with her brother. She hid herself behind a glass door. Do you think her brother will be able to locate her? If yes, why? If no, why not?

Answer: Yes, Shikha's brother will be able to track her down because glass is a transparent material. Transparent substances are those... View Article

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