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Question
Give two examples for the following case:
Physical changes which are not reversible
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Solution
- Cutting of paper
- Breaking of glass
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Try segregating the things around you as pure substances or mixtures.
Photosynthesis cannot take place at night.
True or false
Is melting of ice a reversible change?
Which of the following are physical changes ?
- melting of iron metal
- rusting of iron metal
- bending of an iron rod
- drawing a wire of iron metal
Which of the following are chemical changes ?
- decaying of wood
- burning of wood
- sawing of wood
- hammering of nail into wood
Classify the Following as a Physical Or a Chemical Change.
Making of a Sugar Solution
State the observations seen, when milk in a dish is kept aside for a few hours or more. Is the change which occurs – a physical change or a chemical change. Give reasons.
Ice kept in a beaker, slowly melts and turns into water. The water in the beaker on solidification is freezing turns back to ice. Give four reasons why the change from ice to water and water back to ice is considered a physical change.
Match the following
| Sr. No. | A | B | C |
| 1. | Melting | Change of state from liquid to solid | Ticking of clock |
| 2. | Condensation | Change of state from liquid to gas | Formation of ice cube |
| 3. | Evaporation | Change of state from solid to liquid | Collecting flowers |
| 4. | Freezing | Change of state from gas to liquid | Ice cube to water |
| 5. | Periodic change | Occurs at irregular time intervals | Water to steam |
| 6. | Non-periodic change | Occurs at regular time intervals | Steam to water drops |
Match the items of Column I with the items of Column II.
| Column I | Column II | ||
| (a) | Large crystals | (i) | Turns lime water into milky |
| (b) | Depositing a layer of zinc on iron | (ii) | Physical change |
| (c) | Souring of milk | (iii) | Rust |
| (d) | Carbon dioxide | (iv) | Sugar candy (Mishri) |
| (e) | Iron oxide | (v) | Chemical change |
| (f) | Dissolving common salt in water | (vi) | Galvanisation |
