Concept:A price tag is the small label attached to an item that states the amount the buyer must pay.
Explanation:The missing phrase should identify the label showing how much an item costs.
Standard English uses "price tag" as a compound noun.
In a compound noun, the first word "price" works like an adjective describing the second word "tag."
Possessive apostrophes are not needed here because the phrase does not express ownership.
Option A, "price's tag," wrongly adds an apostrophe.
Option C, "prices tag," incorrectly makes the modifier plural.
Option D, "prices' tag," uses a plural possessive, which is also wrong.
Only the singular compound noun "price tag" fits the sentence naturally.
Answer:B. price tag