Which element has the lowest electronegativity, and how can you answer this question without looking up electronegativity values? (a) \(\mathrm{Mg}\) (b) \(\mathrm{Cl}\) (c) \(\mathrm{Ca}\) (d) \(\mathrm{Br}\)

To figure out electronegativity trends, we first need to identify the group and period of each element in the periodic table. (a) Mg (Magnesium): Group 2, Period 3 (b) Cl (Chlorine): Group 17, Period 3 (c) Ca (Calcium): Group 2, Period 4 (d) Br (Bromine): Group 17, Period 4

According to the periodic trend, electronegativity increases from left to right along a period and decreases down a group in the periodic table. Comparing Mg and Cl, as they are in the same Period (Period 3), the electronegativity will follow left to right trend. Mg is to the left of Cl, so Mg has lower electronegativity than Cl. Now, comparing Ca and Br, as they are in the same Period (Period 4), the electronegativity will again follow the left to right trend. Ca is to the left of Br, so Ca has lower electronegativity than Br. Finally, comparing Mg and Ca, as they are in the same Group (Group 2), the electronegativity will follow the top to bottom trend. Mg is above Ca, so Ca has lower electronegativity than Mg.

Based on our analysis in steps 1 and 2, we can conclude that Ca (Calcium) has the lowest electronegativity among the given elements. The answer is (c) Ca (Calcium).