Name the densest stable element known on earth.

Osmium

The correct answer is option 3. Osmium.

Osmium, with the chemical symbol Os and atomic number 76, is the densest stable element known on Earth.

Osmium has a density of approximately 22.59 grams per cubic centimeter \((g/cm^3)\) at room temperature and pressure. This makes it the densest naturally occurring element.

Osmium belongs to the platinum group of metals and is located in Group 8 (VIII-B) of the periodic table. It has a dense, closely packed atomic structure, which contributes to its high density.

Due to its high density and other physical properties, osmium has several practical applications. It is used in various fields such as industry, research, and jewelry. For example, osmium alloys are used in specialized electrical contacts, fountain pen nibs, and certain types of surgical instruments. Osmium tetroxide \((OsO_4)\), a compound of osmium, is used in microscopy as a staining agent.

Osmium is relatively rare in the Earth's crust and is often found alongside other platinum group metals, such as platinum and iridium. Its rarity, combined with its dense and valuable properties, makes osmium one of the most expensive and sought-after elements.

In summary, osmium is the densest stable element known on Earth, with a density higher than that of any other naturally occurring element. Its high density and unique properties make it valuable in various industrial and scientific applications