Final answer:
In Freudian theory, the part of the personality that is entirely unconscious and driven by biological instincts is the 'id,' which seeks immediate gratification based on the 'pleasure principle.'
Step-by-step explanation:
In the Freudian view of personality, the part of the personality that is totally unconscious and dominated by biological instincts is known as the id. The id is present from birth and houses our most primitive drives, including impulses for hunger, thirst, and sex, operating on what Freud described as the "pleasure principle." This principle is all about seeking immediate gratification for these urges, without consideration for reality or social norms.
The ego and superego develop in response to social interactions, with the ego acting as the rational component that balances the instinctual demands of the id with the moralistic demands of the superego, which embodies the conscience and values learned from society. While the ego operates on the "reality principle," aiming to satisfy the id's desires in a realistic and socially appropriate manner, the superego is focused on upholding moral ideals. Thus, in Freud's theory, the id is the only component of the personality that is completely unconscious and dominated by instinctual biological drives.