Final answer:
Element Z is the strongest reducing agent because it easily gains 3 electrons.
Step-by-step explanation:
The element that is the strongest reducing agent based on its electron behavior is Element Z, which easily gains 3 electrons. In redox reactions, reducing agents are substances that tend to donate electrons to other substances, causing their oxidation. Since Element Z can easily gain 3 electrons, it is more likely to undergo reduction and act as a reducing agent.