Which of these elements has the most chemically non reactive atoms neon iron lithium bromine

The answer is Neon. The reason Neon is least reactive of all the listed elements is because it is in a group of the periodic table called Noble gases. These are elements whose atoms have a full shell of 8 Valence (outer) electrons. Because they have a full octet they do not need any extra or any less electrons to become stable and so do not bond with other elements unless ionized.