Which part of an atom is known as the valence shell?

The part of an atom known as the valence shell refers specifically to the outermost electron shell. This shell contains the electrons that are involved in chemical bonding and interactions with other atoms. The valence electrons are critical because they determine an atom's reactivity, stability, and the types of bonds it can form with other atoms.

Understanding that the valence shell is the outer layer is essential when studying how atoms combine to form molecules. The properties of an element, including how it will interact with other elements, depend significantly on the configuration of electrons in this outer shell. For example, elements in the same group of the periodic table often have similar properties due to having the same number of valence electrons.

The other parts of an atom mentioned in the options serve different functions. The nucleus, which contains protons and neutrons, is the core of the atom and does not play a direct role in chemical bonding. The inner shell housing electrons that are not involved in bonding is referred to as core electrons. The term "core" itself does not refer to a specific part of the atom related to bonding. Understanding the distinctions among these terms is key for grasping concepts in physical science related to atomic structure and reactivity.