This week, Graihagh Jackon drilled into John's question to try and find out what the most expensive element in the world is... But first, how do we define 'expensive?' Chemist Mark Lorch set us straight... Like this podcast? Please help us by <a href="https://www.thenakedscientists.com/donate">supporting the Naked Scientists</a>

How much of a wheat field do I need to make one loaf of bread?

Each week we set out to solve one of the world's weirdest, wackiest, funniest and funkiest scientific puzzles. And along with the answer there's a brand new question to think about for next time...