Here's why:

* Alloy in Ballpoint Pens: Tungsten carbide is a very hard and durable material, making it ideal for the ballpoint in pens.

* Density: Tungsten is nearly twice as dense as lead.

* Toxic Oxide: Tungsten trioxide (WO3) is the primary oxide of tungsten. It has a strong odor and is highly toxic.

Let me know if you have any other questions!