Taking into account the definition of reactivity, the correct option is the first option: Metals on the right have more valence energy levels, so the ability of the nucleus to attract electrons is reduced.
Reactivity is a measure of the probability that a chemical species will participate in a chemical reaction to form chemical bonds.
In other words, the reactivity of a chemical element is the tendency that this element has to combine with others.
For elements that behave like metals, this trend is directly related to the ease with which they lose their valence electrons.
Valence electrons are those electrons farthest from the nucleus of the atom. These electrons are easier to remove because they are the least attracted to the nucleus. Thus, less and less energy is needed to start these valence electrons, so they can commonly participate in the formation of chemical bonds.
In other words, as the size of the metal atoms in a group increases, so does their reactivity.
Then, the correct option is the first option: Metals on the right have more valence energy levels, so the ability of the nucleus to attract electrons is reduced.
Learn more: