Explanation:
As it is known that in solids, molecules are held together because of strong intermolecular forces of attraction. As a result, they are held together and have definite shape and volume.
Whereas in liquids, molecules are not held so strongly as they are in solids. Hence, they move from their initial position and they do not have definite shape but they have definite volume.
Liquids obtain the shape of container in which they are kept.
In gases, molecules are held together by weak intermolecular forces. As a result, they move far apart from each other and occupy the space of a container or vessel in which they are placed.
The physical state (at room temperature) of the following are determined as follows:
(a) Helium in a toy balloon : Helium at room temperature exists as a gas. So, when helium is present in a toy balloon then it acquires the volume of toy balloon.
(b) Mercury in a thermometer : Mercury at room temperature exists as a liquid. When it is placed in a thermometer then volume of mercury does not get affected.
(c) Soup in a bowl : Since, soup is a liquid. Hence, its volume will not change according to the volume of container.
