Explanation:

- Capital loss: This occurs when the value of an asset decreases in comparison to its purchase price. It is not related to an increase in the stock of capital.

- Capital gain: This refers to the profit made from selling an asset for more than its purchase price. It’s also unrelated to an increase in the overall stock of capital.

- Capital formation: This is the process of increasing the stock of physical capital in an economy by investing in new assets such as machinery, tools, and buildings. It directly refers to increasing the overall capacity and efficiency of production.

- None of these: Used when none of the provided options are suitable. However, in this case, option 3 is correct.