Misc: What French emperor died in Kent?

Questions

Which number could not be represented in the Roman numbering system?

Which chemical element emits a greenish glow in air, and, unless kept in water, burns of its own accord?

Which single word connects a Beethoven composition, a Glenn Miller melody and some Terry's chocolates?

What is the venue for the coursing Waterloo Cup?

What is the name of the Buckinghamshire estate where the German Enigma codes were cracked during World War 2?