Element a has seven valence electrons. how does its reactivity compare to that of element b, which has four valence electrons?

The correct answer is "Element A is more reactive".

Explanation:

The missing options of this question are:

Element A is more reactive.

Element A is less reactive.

Element A and B have the same reactivity.

Element A has no reactivity.

The correct answer is "Element A is more reactive".

Valence electrons are defined as outer shell electron that can participate in the formation of chemical bonds with other atoms. The atoms tend to have either 0 or 8 valence electrons. Therefore, depending in the number of valence electrons, an atom can either give their valence electrons (1 to 3 electrons) or try to take more valence electrons (4 to 7 electrons). Element A with 7 valence electrons is more reactive that Element B with 4 valence electrons, because Element A only needs 1 more electron to full its 8 valence electrons.