From the given options, select the figure of speech (poetic device) used in expression:

The stagnant ocean was like a blue film

Simile

The correct answer is simile.

Simile is a figure of speech in which two things are compared using the words "like" or "as." In the expression "The stagnant ocean was like a blue film," the ocean is compared to a blue film. This creates a sense of the ocean being still, lifeless, and voyeuristic.

The other options are incorrect. Personification is the attribution of human qualities to inanimate objects or animals. Oxymoron is a figure of speech in which two contradictory terms are combined to create a new meaning. Pun is a play on words, often involving a homophone.