ICSE ICSE Class 8 - CISCE Question Bank Solutions

If an atom ‘A’ has an atomic number of eleven, state the number of protons and electrons it contains.

State how electrons are distributed in an atom. Explain in brief the rules which govern their distribution.

Select the correct answer from the choice in the bracket to complete the sentence:

An element ‘X’ has six electrons in its outer or valence shell. Its valency is __________.

Select the correct answer from the choice in the bracket to complete the sentence:

A ________ is a sub-atomic particle with no charge and unit mass.

Select the correct answer from the choice in the bracket to complete the sentence:

Magnesium atom with electronic configuration 2, 8, 2 achieves stable electronic configuration by losing two electrons, thereby achieving stable electronic configuration of the nearest noble gas _______.

Change is the law of nature which occurs in everyday life.
State when a substance [i.e. matter] undergoes a kind of change. 

Give a reason why

Freezing of water is a reversible change while burning of a candle – an irreversible change.

Give a reason why

Change of seasons is a periodic change while the change of weather is a non-periodic change.

State which of the following pertain to – chemical changes.

1. Substance retains its identity.
2. The change is permanent.
3. No new substance is formed.
4. Is easily reversible.
5. Produces one or more new substances by a change in its composition.
6. The change is temporary.
7. The composition and properties of the original substance are not altered.

Give four reasons why the burning of a magnesium ribbon in the air is considered a chemical change.

Compare the energy changes involved during a physical and a chemical change.

Is a change of state of matter – a physical or a chemical change. Give reasons.

State which of the following terms connected with change of state of matter i.e.

(a) Melting
(b) Vaporisation
(c) Condensation
(d) Freezing

pertain to –

1. Conversion of a liquid into a vapour or gas.
2. Conversion of a liquid into a solid.
3. Conversion of a solid into a liquid on heating.

Potassium chloride is added to water and stirred. A salt solution is obtained, which is then boiled, leaving behind a residue.

1. Is the above change physical or chemical?
2. Name the residue which remains behind after the salt solution is boiled.
3. Is the change reversible or not reversible?
4. Are the composition and properties of the original substance altered?
5. Give a reason why the above experimentation would not be possible if calcium carbonate was taken in place of potassium chloride.

Give a reason why – Heating a platinum wire is a reversible change but, heating a magnesium wire is an irreversible change.

Give a reason why – Addition of zinc nitrate to water is a physical change but, the addition of zinc to dilute nitric acid is a chemical change.

Give a reason why rusting of iron is a chemical change but, the magnetization of iron is a physical change.

Select the chemical changes from the following list of changes

Vaporisation of water into water vapour.

Select the chemical changes from the following list of changes

Boiling of milk. 

Select the chemical changes from the following list of changes

Respiration in mammals.