Explanation:

- Option 1: Act of Becoming Free is not typically associated with the symbol of a snake biting its tail.

- Option 2: Strength lies in Unity doesn't capture the essence of the snake forming a circle.

- Option 3: Knowledge, while a powerful concept, is not linked to this particular symbol.

- Option 4: Eternity is correct. The symbol of a snake biting its own tail to form a ring is known as the Ouroboros. It represents the cycle of life, infinity, and the eternal return in various cultural contexts.