Answer:

Introduction:
In this question, we are asked to identify the heaviest metal among iron, silver, nickel, and osmium. In order to determine the correct answer, we need to consider the atomic masses of these metals.

Explanation:
Let's examine each metal individually to determine its atomic mass and understand why osmium is the heaviest metal among the given options.

1. Iron:
The atomic mass of iron is approximately 55.845 atomic mass units (u). Iron is a relatively heavy metal, but it is not the heaviest among the given options.

2. Silver:
The atomic mass of silver is approximately 107.8682 u. While silver is a valuable metal, it is not as heavy as some other options.

3. Nickel:
The atomic mass of nickel is approximately 58.6934 u. Nickel is a relatively heavy metal, but it is still not the heaviest among the given options.

4. Osmium:
The atomic mass of osmium is approximately 190.23 u. Osmium is known for being extremely dense and heavy, making it the heaviest naturally occurring element. It has a high atomic mass, which makes it significantly heavier than iron, silver, and nickel.

Conclusion:
Based on the atomic masses of the given metals, it can be concluded that osmium is the heaviest among iron, silver, nickel, and osmium. With an atomic mass of approximately 190.23 u, osmium surpasses the other metals in terms of weight.