Final answer:
Potassium (K) from group 1, the alkali metals, is the most chemically reactive element among those listed due to its high tendency to lose its outer electron and vigorous reaction with water.
Step-by-step explanation:
Among the options provided – zinc (Zn), iron (Fe), potassium (K), and germanium (Ge) – potassium is the most chemically reactive. Potassium is a member of the alkali metals (group 1 of the periodic table), which are known for their high reactivity. Alkali metals readily lose their single outer electron to form cations, and they react vigorously with water to form hydrogen gas and a basic solution of the metal hydroxide. In contrast, the other options belong to different groups and are not as reactive as group 1 metals. Zinc and germanium react more slowly with air due to the formation of a protective oxide film, and iron, while reactive, does not display the same level of reactivity as the alkali metals.