Final answer:
Reactivity increases when moving from atomic number 10 (Neon) to atomic number 11 (Sodium) due to the decrease in ionization energy and the ease of losing the lone valence electron in these elements.
Step-by-step explanation:
Moving from the element with atomic number 10 (Neon) to the element with atomic number 11 (Sodium) on the periodic table, there is a significant change in reactivity. The correct statement that best describes this change is C) Reactivity increases. This increase in reactivity is attributed to the ease with which these elements can lose their lone valence electron. As atomic number increases, especially in elements in groups 1 and 2 of the periodic table, the ionization energy decreases. This facilitates the loss of electrons and thus enhances reactivity. The alkali metals in group 1 are known for being very reactive metals, an attribute underpinned by their large atomic radii and low ionization energies, which allow their outermost electron to be removed easily.