<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.
Answer: The mass of electrons is mostly ignored because electrons are extremely small compared to neutrons and protons.
Explanation: A proton is about 1,836 times the size of an electron.
On the periodic table, the atomic number for each element can be found. This number is found by measuring the weight of 6.02 x 10^23 atoms of the element in grams. Electrons aren't ignored when finding exact math, but for the sake of simplification high school teachers will generally have you only count the number of protons and neutrons when calculating the mass of atoms.
I believe is different in pressure