From the given options, select the Figure of Speech (Poetic Device) used in the expression:

As clear as crystal

Simile

The figure of speech used in the expression "As clear as crystal" is simile.

A simile is a figure of speech in which two things are compared using the words "like" or "as." In this case, the clarity of something is being compared to the clarity of crystal. This creates a sense of the thing's transparency and purity.

The other answer choices are incorrect. Metaphor is a comparison between two things without using the words "like" or "as." Pun is a play on words. Oxymoron is a figure of speech in which two contradictory terms are used together. None of these devices are used in the expression "As clear as crystal.".