Iron, cobalt and nickel are collectively called as `"…................"` metals.

Answer

**Step-by-Step Solution:**

1. **Identify the Metals**: The question asks about iron, cobalt, and nickel. These are transition metals found in the d-block of the periodic table.

2. **Understand the Grouping**: These three metals are often grouped together due to their similar properties. They are known for their ability to form various oxidation states and complex ions.

3. **Common Name**: The collective name for iron, cobalt, and nickel is "ferrous metals." This term is derived from the Latin word "ferrum," which means iron.

4. **Conclusion**: Therefore, the answer to the question is that iron, cobalt, and nickel are collectively called "ferrous metals."

**Final Answer**: Iron, cobalt, and nickel are collectively called "ferrous metals."

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