In order to solve this question, we can use the electronegativity table (or also just a regular periodic table), which will give us the values of electronegativity for each element.
As we can see in this table, the least electronegative element will be Al, with only 1.61 of value. If you were with a regular periodic table, you could find this answer by thinking about the periodic table trend, or we can also call it a rule, that in most elements the electronegativity will grow in value from left to right and from the bottom to the top, then you would also get Al as your answer
Answer = Al, letter D