Mass, if you know what element you are working with.
<u>Answer:</u> The outermost valence electron enters the p orbital.
<u>Explanation:</u>
Valence electrons are defined as the electrons which are present in outer most orbital of an atom.
Sulfur is the 16th element of the periodic table having 16 electrons.
Electronic configuration of sulfur atom is 
The number of valence electrons are 2 + 4 = 6
These 6 electrons enter s-orbital and p-orbital but the outermost valence electron will enter the p-orbital.
Hence, the outermost valence electron enters p orbital.