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Which one of the following forms of energy leads to the least environmental pollution in the process of its harnessing and utilisation? (a) Nuclear energy (b) Thermal energy (c) Solar energy (d) Geothermal energy

Answer: (c) Solar energy Solar energy is the natural source of energy from solar power absorbed from the sun through solar panels. Once the... View Article

Which is the ultimate source of energy? (a) Water (b) Sun (c) Uranium (d) Fossil fuels

Answer: (b) Sun The sun, either directly or indirectly, is the ultimate source of almost all types of energy on Earth. Coal, oil, and gas are the... View Article

In a hydropower plant (a) Potential energy possessed by stored water is converted into electricity (b) Kinetic energy possessed by stored water is converted into potential energy (c) Electricity is extracted from water (d) Water is converted into steam to produce electricity

Answer: (a) Potential energy possessed by stored water is converted into electricity Hydroelectric power plants convert the potential energy of... View Article

Fuel used in thermal power plants is (a) water (b) uranium (c) biomass (d) fossil fuels

Answer: (d) fossil fuels Coal is the major fossil fuel used in thermal power plants. Along with coal natural gas and petroleum are also used.... View Article

Acid rain happens because (a) sun leads to heating of the upper layer of the atmosphere (b) burning of fossil fuels release oxides of carbon, nitrogen and sulphur in the atmosphere (c) electrical charges are produced due to friction amongst clouds (d) earth atmosphere contains acids

Answer: (b) burning of fossil fuels release oxides of carbon, nitrogen and sulphur in the atmosphere Acid Rain is defined as the precipitation of... View Article

Which of the following is a non-renewable source of energy? (a) Wood (b) Sun (c) Fossil fuels (d) Wind

Answer: (b) Sun Non-renewable source of energy are obtained from the earth’s crust and once used they disappear. These resources cause... View Article

A student took a solution of copper sulphate in a beaker and put a clean iron nail into it and left it for about an hour. (a) What changes do you expect? (b) Are these changes chemical in nature? (c) Write a word equation for the chemical change, if any.

Answer: (i) Colour of the solution in the beaker changes from blue to green. (ii) A brown coloured deposit is found on the surface of the... View Article

If you leave a piece of iron in the open for a few days, it acquires a film of brownish substance, called rust. (a) Do you think rust is different from iron? (b) Can you change rust back into iron by some simple method? (c) Do you think the formation of rust from iron is a chemical change? (d) Give two other examples of a similar type of change

Answer: (a) Rust is iron oxide and it’s different from iron (b) Formation of rust is irreversible hence it cannot be reversed by any... View Article

Give an example of a chemical reaction for the following situation: Sound is produced.

Answer: Cracker on ignition produces sound due to the sudden formation of a large amount of gas due to chemical reactions, such a reaction is... View Article

Give an example of a chemical reaction for the following situation: Gas is evolved.

Answer: In the reaction between baking soda and vinegar, carbon dioxide is evolved. When heated, baking soda gradually decomposes to form sodium... View Article

Give an example of a chemical reaction for the following situation: A change in colour is observed.

Answer: The reaction between copper sulphate solution and iron metal When an iron nail is immersed in the solution of copper sulphate then iron... View Article

Give two examples for the following case: Chemical changes.

Answer: Physical change – A substance is said to undergo a physical change when only the physical properties such as the shape, size,... View Article

Give two examples for the following case: Physical changes are not reversible.

Answer: Physical change – A substance is said to undergo a physical change when only the physical properties such as the shape, size,... View Article

Give two examples for the following case: Physical changes are reversible.

Answer: Physical change – A substance is said to undergo a physical change when only the physical properties such as the shape, size,... View Article

Explain : Bubbles are produced when acetic acid is added to a solution of sodium hydrogen carbonate.

Answer: Carbon dioxide is evolved due to the chemical reaction between acetic acid and sodium hydrogen carbonate. The reaction of this statement... View Article

Write word equations for two chemical reactions with the help of materials given in the box. [Air, copper sulphate, iron, vinegar, iron oxide, carbon dioxide, iron sulphate, copper, lime water, water]

Answer: A chemical reaction is in which the bonds are broken within reactant molecules, and new bonds are formed within product molecules in... View Article

Classify the following processes into physical or chemical changes: (i) The beating of aluminium metal to make aluminium foil. (ii) Digestion of food. (iii) Cutting of a log of wood into pieces. (iv) Burning of crackers.

Answer: Physical change - The type of change in which the physical properties of a material change. It can be changed in shape, state of matter,... View Article

(a) Making sugar solution is a ____ change. (b) A physical change is generally. (c) Grinding of wheat grain changes its size. It is a change. (d) Iron benches kept in lawns and gardens get. It is a _ change because a new _____ is formed.

Answer: Physical change - The type of change in which the physical properties of a material change. It can be changed in shape, state of matter,... View Article

What kind of change is shown by tearing of paper?

Answer: Tearing paper is a physical change that cannot be reversed. Physical change - The type of change in which the physical properties of a... View Article

Melting of wax is a change where a solid changes to a liquid state. Give one more such change which you observe in your surroundings.

Answer: Physical change - The type of change in which the physical properties of a material change. It can be changed in shape, state of matter,... View Article

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