To find the incorrectly spelled word, we need to check the spelling of each option carefully.
Step 1: Check Option A - Conscientous
The correct spelling is "Conscientious,'' which means wishing to do one's work or duty well and thoroughly.
"Conscientous'' is a misspelling missing the letter 'i' before "ous.''
Hence, Option A is spelled incorrectly.
Step 2: Check Option B - Peculiar
"Peculiar'' is correctly spelled. It means strange or odd; unusual.
Step 3: Check Option C - Accommodate
"Accommodate'' is correctly spelled. It means to provide lodging or sufficient space for.
Step 4: Check Option D - Repetition
"Repetition'' is correctly spelled. It means the action of repeating something.
Therefore, the only incorrectly spelled word is Option A: "Conscientous.''