Final answer:
Fluorine (F) is the element in period 3 with high electronegativity and seven valence electrons that tends to steal one electron.
Step-by-step explanation:
The element in period 3 with high electronegativity and seven valence electrons that tends to steal one electron is Fluorine (F).
Fluorine has an atomic number of nine and belongs to Group 7A (the halogens) on the periodic table. It has seven valence electrons and a high electronegativity of 4.0, making it highly likely to gain one electron to achieve a noble gas configuration. When fluorine gains an electron, it becomes a negatively charged ion known as fluoride (F-).
Therefore, the correct answer is c) Fluorine.