What is a Valence Electron? & how to identify the valence electron for an atom?

Valence electrons are the electrons in the outermost shell, or energy level, of an atom

Explanation:

For example, oxygen has six valence electrons, two in the 2s subshell and four in the 2p subshell. We can write the configuration of oxygen's valence electrons as 2s²2p⁴.

For neutral atoms the number of valence electrons is equal to the atom's main group number. The main group number for an element can be found from its column on the periodic table. For example, carbon is in group 4 and has 4 valence electrons. Oxygen is in group 6 and has 6 valence electrons.

particle   p is an electron and particle q is a neutron