Why the solid are rigid, incompressible, definite shape, definite volume, higher density, intermolecular force are strong, diffusion of a solid into another solid is extremely slow ?

 Solid are rigid and incompressible:

Solids are rigid and incompressible. Because the constituent particles are closely packed and there is no space between the particles. That is why solids cannot be compressed. A sponge can be compressed easily because it has small pores in it. Air is trapped in these pores. When a sponge is pressed, air is released out and it gets compressed. 

Solid has a difinite shape and volume:

A solid has a difinite shape and volume. Because the constituent particles are held together by a strong attraction force. For example, sugar and salt are solids because the shape of each individual crystal remains unchanged.

Solids in general have higher density:

Solids have higher density than liquids and much higher than that of gases. This is because the particles in solids are packed tightly due to strong intermolecular forces. Density is defined as mass per unit volume.

In solids, Intermolecular force are strong:

 In solids, the constituent particles are held closely in fixed positions due to a strong force of attraction. These particles, however can rotate and/or vibrate about their mean positions. Thus, the particles in solids possess very little kinetic energy. 

fusion of solid into another solid is extremely slow:

The particles in solids do not move much from their fixed positions. Therefore, diffusion of one solid into another is extremely slow.