Answer
B. The valence shell is the outermost layer of electrons in an atom.
D. Electrons are located in layers around the nucleus.
Step-by-step explanation
Atomic structure refers to the structure of an atom comprising a nucleus (center) in which the protons (positively charged particles) and neutrons (neutral) are present. The negatively charged particles called electrons revolve around the center of the nucleus.
Therefore, among the given statements, the correct statements about atomic structure are:
B. The valence shell is the outermost layer of electrons in an atom.
D. Electrons are located in layers around the nucleus.