Select the appropriate article to complete the following sentence. Choose…

Concept

• Indefinite article ("a"/"an") -- used before a singular countable noun that is being introduced for the first time (not previously identified); choose "a" before a consonant SOUND and "an" before a vowel SOUND (the sound decides it, not the spelling).

• Definite article ("the") -- used before a noun that refers to something specific, already identified earlier in the discourse, or unique/one-of-a-kind.

• Zero article (no article) -- used with uncountable nouns, general/generic plural nouns, or proper nouns -- not with a singular countable common noun that still needs a determiner.

Application

1. "Death" here is a singular countable noun used in the fixed cognate-object pattern "die a [adjective] death" (compare "die a natural death", "die a hero's death"), so it needs a determiner -- the zero article is ruled out.

2. The death being described has not been mentioned or identified earlier in the sentence, so the definite article "the" (which points to something already specific or known) is ruled out too.

3. That leaves the indefinite article, and the choice between "a" and "an" depends only on the SOUND that follows: "peaceful" begins with the consonant sound /p/.

4. A consonant sound takes "a", not "an" -- so the blank must be filled with "a": "He died a peaceful death."

Cross-check

Substituting "an" produces the ungrammatical "an peaceful death" (an indefinite article chosen for a vowel sound never precedes a consonant sound in standard English). The fixed idiom itself is consistently written with the indefinite article in standard usage, e.g. "die a natural/violent/peaceful death" -- confirming "a" is the correct choice.