usually it is the second to third layer of electrons. it depends on what atom ur talking about, some atoms (like magnesium) have 3 electron levels; when some atoms (like gold) may have over 7 levels...
an electron is a wavelength of energy that orbits a nucleus at the speed of light in an orbital where only one other electron can exist with an opposite spin, the electons in the orbitals in the...
Heterochromatin is more densely packaged than euchromatin and is much less transcriptionally active. Examples of heterochromatic DNA would be the centromeric and telomeric regions of a chromosome.