The correct option is
C Indifferent
The word 'officious' refers to feeling assertive of authority in a domineering way, especially with regard to trivial matters.
Option A, restrained is characterized by reserve or moderation.
Option B, unofficial refers to feeling not officially authorized or confirmed.
Option C, indifferent refers to having no particular interest or sympathy. Thus, according to the meaning of the given word, this will be the correct antonym to 'officious'.
Option D, detached refers to feeling separate or disconnected.