See here question has answer in itself
The structural isomerism starts always from but word root .
So butane has one and most among all as rest three have none .
The two isomers are
Noble gases are the least reactive of all elements. That's because they have eight valence electrons, which fill their outer energy level. This is the most stable arrangement of electrons, so noble gases rarely react with other elements and form compounds.
Answer:
it is released as lower energy
