Where are valence electrons located? in both the inner and outer electron shells in the outermost electron shell closest to the nucleus inside the nucleus

In outer most electronic shell.

Explanation:

The electrons present in outer most shell or higher energy level are valance electrons, while the electron present in inner most shell or lower energy level are called core electrons.

The valance electrons take part in bonding. The valance electrons form either a ionic bond or covalent bond during chemical reaction. These electrons involve in bond making and bond breaking process.

Example:

Consider the example of carbon. The atomic number of carbon is six.

Electronic configuration:

1s² 2s² 2p²

In this electronic configuration we can see that two electrons are present in 1s shell these are called core electrons. The electrons present in 2s and 2p are called valance electrons and take part in chemical reaction.

the number of valence electrons for each molecule or ion is shown beneath the structure. remember hydrogen will not have more than two electrons. this hydrogen is part of a covalent bond (sharing two electrons). a double bond here would cause hydrogen to share four electrons with phosphorus.