Final answer:
The item 'b. Investment in common stock' is not considered an operating asset when calculating ROI, as it represents financial capital. Operating assets include items used in day-to-day operations, unlike investments in common stock.
Step-by-step explanation:
The item that is not considered an operating asset for the purposes of calculating return on investment (ROI) is b. Investment in common stock. Operating assets are used in the day-to-day operations of a business to generate revenue. Examples include inventory and plant equipment. Conversely, cash and investments such as common stock are considered financial capital, which represents claims on future payments and cannot be used directly in the production of goods and services. While cash and investments can be used indirectly to acquire factors of production, they are not themselves operating assets.
Money, while essential for business operations, is not considered capital because it cannot be used directly to produce other goods. However, money is a form of financial capital and can be utilized to purchase operating assets, which are the physical or intangible assets used continuously in the business's operations.