(a) The ability of a substance to flow is called fluidity. Fluidity is only possible if there is enough space among the particles of the substance and the inter-molecular forces must not be very strong.

Solids have very strong inter-molecular forces of attraction among the particles forming it. They tend to maintain shape and have fixed volume.

Liquids and gases have weak inter-molecular forces of attraction when compared to solids. Hence, they have a tendency to obtain the shape of the container in which they are kept.

(b) Kinetic energy is the energy associated with the motion of particles. In solids, the particles do not move much due to strong inter-molecular forces of attraction. Therefore, the kinetic energy of the particles of solid is very low.

In liquids, particles can move, but there still is a force of attraction among them. The kinetic energy of particles of liquid is greater than that of solids.

In gases, there are weak inter-molecular forces of attraction among the particles. They are able to move very freely within the container in which it is kept. Therefore the kinetic energy of particles is high in gases.

The order of increase in kinetic energy of the particles of the matter is:

Solid<Liquid<Gas

(c) Density refers to the amount of matter present in a given volume. Density increases with increase in the inter-molecular forces of attraction among the particles forming the matter which leads to more number of particles within the given space.

Since the order of strength of inter-molecular forces of attraction is:

Gases<Liquids<Solids

The increase in order of density for different states of matter is given by:

Gases<Liquids<Solids

(d) The shape of a substance is determined by the packing of particles which is due to the strength of inter-molecular forces of attraction among them.

In solids, particles are tightly packed as there are strong forces of attraction of particles. Hence solids have a fixed shape.

In liquids, particles are loosely packed. As a result, liquids do not have a fixed shape, but they take the shape of the container in which it is kept.

Gas particles are more loosely packed when compared to liquids due to weak forces of attraction. Therefore gases too do not have a fixed shape.

(e) Rigidity is the property of a substance to retain shape. Solids tend to maintain a fixed shape when subjected to external forces. Liquids have a tendency to obtain the shape of the container in which they are kept as the particles are loosely packed.

The particles of a gas are linked by weak forces of attraction. Thus gases do not have a fixed shape.

The increase in the order of rigidity is as follows:

Gases<Liquids<Solids

(f) A substance is compressible only if there is enough space between particles of the substance.

In solids, the particles are tightly packed and hence there is very little empty space inside the substance. Therefore, solids are very difficult to be compressed.

In liquids, there is some space between the particles and is compressible, but it requires a high amount of pressure to compress them.

In gases, there is a large space between the particles and hence is highly compressible.