The correct answer is option C, the periodic table and a chemistry website.
Maria is researching a family of elements so besides her school textbook, Maria should refer to the periodic table and a chemistry website.
In the periodic table a family of elements such as the halogen or inert gases are grouped together based on their atomic number and periodicty of their properties. Maria can observe and learn about their periodic properties such as atomic radii, electronegativity, ionization potential, nature of bonding, and more.
Also a chemistry website that discusses the physical and chemical properties of a family of elements would be relevant.