Determining when a particular identity becomes important for defining the self, as opposed to other identities is:

identity formation

Explanation:

Identity formation may be defined as the mental representation of a person of what they are and who are they. Is a kind of individuation which relates to the development and growth of the distinct personality of any individual.

It is described by Erik Erikson in the theory of the developmental stages in a person. He believes that it is an important task of adolescence.

Thus when any certain identity is important to define oneself which is opposed to the other identities is called as identity formation.

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