Rhenium

A new element with the atomic number 75 was discovered and named rhenium. It was the last element with stable isotopes to be found. They also claimed to have discovered element 43, which they named masurium, but this was a mistake.
 Walter Karl Friedrich Noddack, Ida Eva Tacke Germany 1925 Rhenium

A new element with the atomic number 75 was discovered and named rhenium. It was the last element with stable isotopes to be found. They also claimed to have discovered element 43, which they named masurium, but this was a mistake.