The correct answer is Word case as it does not exist in MS Word at all.
As a quick breakdown of how MS Word handles these options:
Sentence case: Available. Capitalizes the first letter of the first word.
Toggle Case: Available. Flips the casing of every letter.
Title case: Not available by this exact name. MS Word performs this function but explicitly names it "Capitalize Each Word".
Word case: Completely Unavailable. This is a distractor option; no such feature exists.
The 5 Official Options in MS Word
When you open the Change Case menu, you are given exactly five specific choices:
Sentence case
lowercase
UPPERCASE
Capitalize Each Word (The actual name for Title Case)
tOGGLE cASE