Final answer:
The atom with the given electron configuration, assuming the typo is corrected, has 5 valence electrons, which are the electrons from the 4s and 3d sublevels.
Step-by-step explanation:
Valence electrons are the electrons in the outermost energy level of an atom and are involved in chemical bonding. According to the given electron configuration 1s22s22p63s23p4s23d3, we need to identify the outermost electrons. The configuration actually seems to contain an error as '3p4s23d3' is not a standard notation, but assuming the correct sequence and based on the highest principal quantum number, the valence electrons would be from the 4s sublevel (2 electrons) and the 3d sublevel (3 electrons), adding up to 5 valence electrons.