FIVE TRUE/FALSE please help

Which of these conditions most likely produces an unstable isotope?

Select all of the statements which are true. electrons are located in shells or orbits around the atom. electrons orbit slowly around the atom. electrons travel in one flat path around the nucleus of an atom. the valence of an atom is determined by the number of electrons in the atom's outermost shell.

Is 343 in the sequence -5, -2, 1, 4, 7