The correct answer is Sulfur (S).
Sulfur has 6 valence electrons because it is located in Group 16 (or the sixth group over if you don’t count the transition metals). This means that one atom of sulfur has 6 electrons in its outermost shell out of 8 total “spots”, which you can count by counting the group numbers (excluding the transition metals) from Group 1 (with one valence electron) to Group 18 (the noble gases with full valence or outer shells).
By this same logic, Carbon (C) has 4 valence electrons and Cesium (Cs) has 1 valence electron, so neither of these is the correct answer.
Hope this helps!