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

A shade of doubt

Metaphor

The figure of speech used in the expression "A shade of doubt" is metaphor.

A metaphor is a figure of speech in which one thing is compared to another thing without using the words "like" or "as." In this case, the abstract concept of doubt is being compared to a physical thing, such as a shadow. This creates a sense of the uncertainty and ambiguity that doubt can bring.

The other answer choices are incorrect. Pun is a play on words. Personification is a figure of speech in which inanimate objects are given human qualities. Alliteration is the repetition of consonant sounds at the beginning of words. None of these devices are used in the expression "A shade of doubt.".