Answer:
Medium of Exchange
Explanation:
A medium of exchange is an instrument used as an intermediary to facilitate the exchange of goods and services. A good medium of exchange must give a fair valuation of the items being traded. Money is a widely accepted medium of exchange.
Almost all items in a market have a monetary value attached to them. A Buyer or seller would easily know the amount of money needed to trade an item. The $50 is being used as a medium of exchange for the purchase of groceries. The seller accepts the money if they agree with the buyer on the quantity of groceries worth $50.
