Question

A group of particles in a magnetic material whose magnetic fields line up with each other is called a ____________?

Answer 1

Magnetic field lines don't start or stop anywhere, they always make closed loops and will continue inside a magnetic material (though sometimes they are not drawn this way). Magnetic field lines naturally bunch together in regions where the magnetic field is the strongest. This means that the density of field lines indicates the strength of the field.
Magnetic field lines never cross.

In other words, is called “field lines”