(a)The most electronegative element in group 6A
Since electronegativity increases moving up a group, we see that oxygen is the most electronegative element in group 6A.
(b) The least electronegative element in the group Al, Si, P
Electronegativity increases to the right, so within a period it decreases to the left. Al is least electronegative in this group.
(c) The most electronegative element in the group Ga, P, Cl, Na
Moving to the right and up, Cl is the most electronegative in this group.
(d) The element in the group K, C, Zn, F that is most likely to form an ionic compound with Ba.
An ionic compound consists of a metal and a nonmetal. Ba is a metal, so we can eliminate K and Zn from consideration immediately. C and F are both nonmetallic elements, but F has more nonmetallic character (further to the right than C) and so would be more likely to form an ionic compound with Ba.