Stocks and flows

Investment represents expenditure on acquiring or creating capital goods during a period. Since the question specifies investment during the year, it is measured over time and is therefore a flow variable. Opening and closing capital stock are measured at particular dates and are stocks. Option B is correct.

The machines, buildings, equipment, and other productive assets existing at a particular point in time together form the country's capital stock. It is a stock because it is measured on a date. Annual investment is a flow that adds to capital stock over a period, so option A is correct.

The amount or balance in an account stated for today refers to money existing at a particular point of time. It is therefore a stock variable. The amount deposited over a period, such as all deposits during a month, would be a flow. The key distinction is the point-in-time reference in the question, so option C is correct.

The total amount deposited this month is measured over the time interval of one month. Any economic quantity measured during a period is a flow variable. It is different from the account balance at the end of the month, which would be a stock measured at one point in time. Therefore, the correct answer is option D, flow.

Wealth is the accumulated value of assets owned at a particular point in time, so it is a stock. Annual income is earned over the course of a year, so it is a flow. In the other options, the order is reversed or both terms do not fit the required order. Thus, wealth and annual income correctly represent stock and flow respectively.

Exports are goods or services sold to other countries during a specified period, such as a month or year; therefore, exports are a flow. Foreign exchange reserves are the accumulated stock of foreign currency and related assets held at a particular date. Hence, option B correctly gives flow first and stock second.

Population recorded on a fixed date, such as 31 March, measures the number of people existing at one point in time, so it is a stock. Births during a year are counted over an interval of time, so they are a flow. The date-based and year-based wording clearly establishes the distinction, making option B correct.

Opening raw material is the quantity of material available at the beginning of the accounting period, so it is measured at a point in time and is a stock. Raw-material purchases during the year are transactions occurring over a period, so they are a flow. Therefore, option C correctly classifies the two items.

A bank loan balance shown in a balance sheet reports the amount still outstanding on a particular reporting date. Since it is measured at that point in time, it is a stock variable. New borrowing or loan repayments made during a year would instead be flows because they are measured over a period. Thus, option B is correct.

Annual interest expense represents the interest cost incurred over the complete period of one year. A quantity measured over a period is a flow variable. It should not be confused with the outstanding loan balance at year-end, which is a stock. The word “annual” establishes the time interval, so option C is correct.

The amount or rate of water moving through a river per second is measured with reference to a time interval. A quantity measured per second, per day, or per year is a flow variable. A stock would be the total water present in a river, lake, or reservoir at a particular moment. Therefore, option A is correct.

The quantity of water stored in a dam at a particular moment is measured at one definite point in time, so it is a stock variable. The water entering or leaving the dam during a day or year would be a flow because it is measured over a period. The phrase “at a moment” makes option B correct.

Gross investment is a flow because it measures the expenditure on newly produced capital goods during a specified period, such as a month or a year. Capital stock is a stock because it measures the total quantity or value of capital assets available at a particular point in time. Investment during a period can add to the existing capital stock, after allowing for depreciation.

“Cash available today” identifies a definite point of time: the present day. It describes the amount existing at that moment and therefore represents a stock. Sales during a year, monthly wages, and annual production are measured over periods and are flows. Thus, option C most clearly indicates a point in time.

“Sales for three months” explicitly identifies a period lasting three months. Sales occurring throughout that interval are measured as a flow. A debt balance at year-end, assets on a date, and a current bank balance are measured at particular points in time and are stocks. Therefore, option D most clearly indicates a period.

The market value of a company stated on a particular date represents the value existing at one specific point in time. Such a quantity is called a stock variable. A flow is measured over a period, such as monthly income or annual expenditure. Therefore, option A is correct.

Service income earned during the whole year is measured over a period of time, so it is a flow variable. A flow records an activity or amount accumulated during a specified interval, such as a month or year. In contrast, a stock is measured at one particular point, such as cash held on the last day of the year. Therefore, option B is correct.

The value of a financial-asset portfolio at the end of a day is measured at a specific point in time. It is therefore a stock variable. Stocks represent holdings or quantities existing at a particular date, whereas income and expenditure are normally flows measured over an interval. Thus, the portfolio is correctly classified by option C.

The total value of shares bought and sold during one day is measured across a time interval, not at a single instant. It is therefore a flow variable. A stock would be the value of shares held at a particular date. The wording “during one day” identifies an activity accumulated over time, so option D is correct.

Annual income is earned and measured over the course of a year, so it is a flow rather than a stock. The other examples are measured at a particular point: cash held today, assets at year-end, and population on a stated date. Since option B wrongly labels a period-based amount as a stock, it is the required answer.

Population measured on the first day of January is measured at one definite point in time, so it is a stock. It is incorrectly labelled as a flow in option C. Monthly wages, annual output, and exports during a year are measured over periods and are therefore flows. Hence, C is the only incorrect classification.

Total consumption expenditure is recorded over a period, such as a month or year, and therefore it is a flow. The value of consumer durables owned by a household is an asset holding measured at a particular point in time, so it is a stock. Consequently, the correct order is flow and stock, given in option B.

Cash held at the end of the day is measured at a particular point in time, so it is a stock. Cash sales made during the day are added over an interval, so they are a flow. The words “at the end” indicate a stock balance, while “during the day” indicates a period total. Therefore, option A is correct.

A daily wage rate refers to earnings associated with work over a time period, so wage income is treated as a flow. Cash held at the end of the month is a balance measured at one point in time, making it a stock. The distinction depends on the time dimension: earning during a period is a flow, while an amount held at a date is a stock. Hence A is correct.

Natural wealth, such as forests, minerals in the ground, and land, represents resources available at a point in time; it is therefore a stock. Annual mineral production is the quantity extracted during a year, so it is measured over a period and is a flow. Hence the correct order is stock and flow, as stated in option B.