An atom has the electron configuration 1s22s22p63s23p1. how many valence electrons does the atom have? valence electrons

            The atom have 3 valence electrons in its valence shell.

Explanation:
                   Electronic Configuration of give atom is,

                                      1s², 2s², 2p⁶, 3s², 3p¹

As the this atom has three energy levels, i.e. 1, 2 and 3 so the valence energy level or Shell is three. In third shell two electrons are present in s orbital and one electron is present in p orbital. So, in total it has three electrons in valence 3rd shell.