Identifying the Correct Preposition for 'Tantamount'

The key phrase in the question is "tantamount __ defiance". The word tantamount is typically followed by the preposition to to indicate equivalence or similarity in significance.

Understanding the Idiom 'Tantamount To'

• The idiom "tantamount to" means equivalent in effect or significance to.
• For example, "His silence was tantamount to an admission of guilt."

Applying the Idiom to the Sentence

In the given sentence, the guidelines are worded meticulously. Any deviation from these guidelines is being equated in seriousness to defiance. Therefore, the correct preposition to complete the phrase is "to".

The completed sentence reads: "The advisory committee issued a set of guidelines so meticulously worded that any deviation would be tantamount to defiance."

Evaluating Other Options

• with: "Tantamount with" is not a standard idiomatic phrase in English.
• for: "Tantamount for" does not fit the meaning of equivalence required here.
• at: "Tantamount at" is grammatically incorrect in this context.

Option 2, to, is the only preposition that correctly completes the idiom "tantamount to".