Which of the following is a flow ?

Depreciation

The correct answer is option (4) : Depreciation

Flow refers to a quantity measured per unit of time, and depreciation fits this definition because it represents the reduction in the value of capital goods over time due to wear and tear, obsolescence, or other factors. It is typically measured annually or over specific periods, making it a flow concept in economic terms.

1. Bank deposits : Bank deposits represent the amount of money held in bank account, and this amount can change frequently as people deposit and withdraw money from their accounts. It is a stock because it represents the movement of money at a point of time.

2. Wealth : Wealth is a stock concept. It represents the total accumulation of assets and  resources at a specific point in time. It doesn't represent a movement over time, but rather the total value of assets and resources at a particular moment.

3. Capital : Capital is also a stock concept. It represents the total assets (such as machinery, buildings, etc.) used in the production of goods and services at a specific point of time. It doesn't represents a flow as it's a snapshot of the total assets, not a movement over time.