Which Porsche 911 should I buy?

From your same page:

Magnesium is only dangerous in shaving or powdered form. It’s dangerous then because the surface area is great enough to allow combustion. Since it’s not relying on an oxygen rich environment to react, water doesn’t help put it out.

Sodium on the other hand is HIGHLY reactive in the presence of water. The contact with water CAUSES the reaction. You CANNOT hold elemental Sodium - it will burn your skin.
Bringin this back on the Porsche topic, and from your page:

I distinctly remember the teacher taking the piece and dropping it into the water, so it couldn’t have been sodium.

Now, where can I buy a piece of pure magnesium…