The correct answer is 3 - Only three.

Let`s break it down:

1. Brand recognition: This is an intangible investment. It`s not a physical asset you can touch, but it takes money and effort to acquire and has value for a company.

2. Inventory: This is not an intangible investment; it`s a tangible investment. You can physically touch inventory, such as products on a store shelf.

3. Intellectual property: This is an intangible investment. It includes things like patents, trademarks, copyrights, which are not physical but hold significant value.

4. Mailing list of clients: This is also an intangible investment. It`s a collection of information that, although isn`t physically touchable, holds value in terms of potential sales and relationships.

Therefore, brand recognition, intellectual property, and a mailing list of clients are intangible investments, whereas inventory is not. Hence, the answer is 3 - Only three.