simply all particles of one substance are identical means just that. all of the particles that make up a piece of matter are the same. an example of this is water. if you look at water under a microscope, you will see that all of the particles that make up the water are identical.

Indistinguishable particles are particles that are so similar or identical that they can not be distinguished from another. Electrons and sometimes atoms and molecules can be indistinguishable particles.

If you think to atoms they are identical.

If you think to atoms they are identical.

P-particles (All matter is made up of particles)

I-identical (All particles in one substance are identical)

S-spacing (There is different spacing between particles of different substances)

A-attraction (Particles have a certain attraction to one another depending on the state)

M-movement (Particles are in constant motion)