Assertion & Reason

Question 11 Mark

Give a reason for the following.
Hard water is not good for washing utensils.

Answer

Reason:
Hard water damages the utensils and containers in which it is stored and forms a hard layer.

Question 21 Mark

Give a reason for the following.
Sea water is unfit for drinking.

Answer

Every litre of sea water contains 35 grams of dissolved salts most commonly known as sodium chloride (NaCl).
Such water is called saline water.
It is not suitable for drinking and is said to be non-potable water.

Question 31 Mark

Give a reason for the following.
Aquatic animals can breathe in water.

Answer

Reason:

Question 41 Mark

Give a reason for the following.
Ice floats on water.

Answer

Reason:

This is because ice is lighter than water.
It means that the density of ice is lower than that of water.
Since ice is a bad conductor of heat it does not allow heat to pass through it.
So, the water below the ice remains in liquid form, where most of the aquatic life lives.

Question 51 Mark

Give a reason for the following.
Water is a universal solvent.

Answer

Reason:

Water has a unique property to dissolve more substances than any other liquids.
It can dissolve solids such as salt and sugar, liquids such as honey and milk, and gases such as oxygen and carbon dioxide in it.
Water can dissolve more number of substances than any other solvent.
Therefore, it is called a universal solvent.

Question 61 Mark

Give a reason for the following.
Alum is added to water in sedimentation tanks.

Answer

Reason:

Chemical substance potash alum is added to water to speed up the process of sedimentation.
This process is called loading.
The particles of potash alum combine with the suspended impurities and make them settle down at a faster rate.

Science Assertion & Reason