Final answer:
Ionization energy is the most useful property in explaining the trend in reactivities in Experiment 1, as it indicates how easily an element can lose electrons, which is a key factor in chemical reactivity.
The correct option is b.
Step-by-step explanation:
In explaining the trend in reactivities in Experiment 1, the most useful property is likely ionization energy (IE). As you move across a row on the periodic table, ionization energies generally tend to increase due to stronger electrostatic interactions between the nucleus and valence electrons.
This implies that elements on the left side of the periodic table lose electrons more easily than those on the right side. Therefore, ionization energy is crucial to understanding why some elements react more readily than others.
Another important property to consider is the atomic radius, which affects the ionization energy. As atomic radii decrease across a period, ionization energy increases, making it harder to remove an electron. This trend is central to predicting reactivities of elements since a larger atomic radius generally means lower ionization energy, thus higher reactivity, particularly for metals.
The electronegativity and metallic character of elements are also essential to understanding trends in reactivity, but ionization energy is often the primary factor in such a comparison. Metallic character helps understand behaviors such as conductivity and malleability, and it is linked to atomic size and ease of losing electrons; however, for non-metals and across periods, ionization energy is a more direct indicator of reactivity.
The correct option is b.