Final answer:
Money serves as a medium of exchange and unit of account when you decide you want "$10 worth" of a product, as you are engaging in a purchase and assigning value to the product.
Step-by-step explanation:
When you decide you want "$10 worth" of a product, money is serving as a medium of exchange because it is being used to buy things. It also serves as a unit of account, which allows for a transaction to be measured and valued. However, in this instance, it's not primarily acting as a store of value because you are choosing to spend the money rather than save it.