Electronegativity generally increases:
a. From Br to K: Electronegativity decreases because electronegativity tends to decrease as you move down a group on the periodic table.
b. From Al to C: Electronegativity increases because electronegativity tends to increase as you move across a period from left to right on the periodic table.
c. From Li to C: Electronegativity increases because electronegativity tends to increase as you move across a period from left to right on the periodic table.
