Final answer:
The correct option is A) the quantity of money is measured at a given point in time.
Money is considered a stock variable because its quantity is measured at a specific point in time. As a store of value, money retains utility over time, despite potential inflation. Money's liquidity allows it to act as an effective medium of exchange and unit of account.
Step-by-step explanation:
When we say that money is a stock variable, we mean that A) the quantity of money is measured at a given point in time. This concept refers to the total amount of money available in the economy at a specific moment, unlike a flow variable, which would be measured over a certain period.
Money's role as a store of value means that it can be saved, retrieved and exchanged in the future, potentially maintaining its value over time. This aspect is important since, despite inflation eroding the purchasing power of money, it still retains its usability as money. The liquidity of money also speaks to its function as a medium of exchange, because its easy convertibility into goods and services without significant loss of value makes it an effective medium for facilitating transactions.
Lastly, the role of money as a unit of account underscores its importance in providing a standard measure for pricing goods and services, simplifying trade and economic calculations.