Ruthenium, pronounced roo-thee-nee-uhm, is one tough element!
It’s not affected by air, water or acid. It does dissolve in household bleach. But don’t try this at home: it gives off some extremely toxic gases as it dissolves. Plus, you don’t want to waste bleach.
Ruthenium is added to metals such as platinum and palladium to harden them.
It can also be used to make other metals more hard-wearing: adding just 0.1% ruthenium to titanium makes it 100 times better at resisting corrosion.
You might find ruthenium in your pencil-case. Some posh Parker Pens have nibs made out of ruthenium, and these are marked ‘RU’.