Question

the electrons in the outermost shell (main energy level) of an atom; these are the electrons involved in forming bonds
alkali metals (group 1)
halogens (group 17)
valence electrons
atomic number

Explanation:

The definition provided ("The electrons in the outermost shell (main energy level) of an atom; these are the electrons involved in forming bonds") matches the term "valence electrons". Alkali metals are group 1 elements, halogens are group 17 elements, and atomic number is the number of protons in an atom. So the correct term is valence electrons.

Answer:

valence electrons