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प्रश्न
Explain the term – ‘sublimation’. Is sublimation of naphthalene – a physical or a chemical change. Give reasons.
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उत्तर
It is the conversion of a solid – directly into gaseous (vapour) state and on cooling directly back to solid-state – without changing into a liquid state.
It involves a change of state-and hence it is a physical change.
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संबंधित प्रश्न
Write short answer.
Give an example of desirable change which can also be undesirable
Solve this crossword by using the clues that follow-
Across
1. Energy in the form of sunlight is absorbed by the green plants in this process.
4. The reddish-brown substance formed over iron in the presence of oxygen and moisture.
5. This change is permanent and irreversible.
6. The process in which a solid directly changes into gaseous state.
Down
1 . It is the change that takes place in case of swinging pendulum of a clock. –
2. Occurrence of this is a non-periodic change as well as a natural change.
3. It is a physical change.
Classify the following as physical or chemical change :
Formation of curd from milk
Fill in the blank.
The process of a liquid changing into a solid is called ________
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.
Fill in the blank with the appropriate word of the statement given below:
If a change is permanent and irreversible it is considered a _________ change.
Give a reason why
Freezing of water is a reversible change while burning of a candle – an irreversible change.
State which of the following pertain to – chemical changes.
- Substance retains its identity.
- The change is permanent.
- No new substance is formed.
- Is easily reversible.
- Produces one or more new substances by a change in its composition.
- The change is temporary.
- The composition and properties of the original substance are not altered.
Is a change of state of matter – a physical or a chemical change. Give reasons.
______ is the substance that is dissolved in a solvent.
