This is called the critical period. The critical period itself is a stage of the development in the life of a human being in which is said that skills are most easily and most readily learned and acquired. This period usually varies for different things like binocular vision and language, but it is said that after the critical period the skills are acquired with much difficulty if they are to be acquired at all.
The anion that would be expected to be most stable than of
others is the iodine. It is because base on its electronegativity, it has the
least electronegativity property compared of other anions and when there is
less electronegativity, it is considered to be the most stable.