Which is the first element to have 4d electrons in its electron configuration?

The first element to have 4d electrons in its electron configuration is Yttrium with an atomic number of 39 and the chemical symbol Y. The electron configuration of an atom refers to the distribution of its electrons in the atomic orbitals. These orbitals are represented by letters s,p,d,f and so on. The electron configuration of Yttrium is [Kr] 4d¹ 5s², wherein [Kr] refers to the electron configuration of the noble gas, Krypton.