Name 5 descriptions of a key including mass

I'm assuming you're talking about something like a regular housekey, in which case there are numerous things you can describe!

Its mass: how much it weighs, times the gravity of the system.

Its color: is it silver-colored, or gold, etc.?

Its volume: you could probably calculate this, though it would be hard because it's not a traditional shape, I assume.

Its density: this is mass/volume. It means how many of the atoms are in a given space; how tightly packed the atoms are.

Its tendency to rust / its specific combination of metals or alloys: is it made of copper, tin, steel ... and these are all things that can rust to varying degrees.