The list of elements from increasing electronegativity: Calcium < magnesium < chlorine < argon < boron.
Explanation:
In the periodic table if you move from left to right there would be an increase in the electronegativity of the elements. If you move from the bottom to the top of the groups in the periodic table the electronegativity increases and if u move to the bottom from down its decreases.
Calcium is in the 2nd group below magnesium so calcium is the least electronegative among given elements then magnesium and then chlorine as it is top of magnesium then argon, as it is right to the chlorine, and boron has the most electronegativity as it is above rest of the elements.
