What electron configuration makes an atom stable and not likely to react?

Ne ( Neon)

Explanation:

Neon has 8 valence electrons.  This is known as the stable octet.  All the Noble Gases, Group 18, have stable outer electron configurations.  

b.final

a. energy is absorbed in the reaction.

if in a given reaction the energy of products is greater than the energy of reactants it means that reaction is endothermic and during the reaction, the energy is absorbed by reactants. in an endothermic reaction, the products have more stored chemical energy than the reactants. and in this reaction the reactants are more stable than products before the compounds with less energy are always more stable.