UPSC 2015 CDS I GK Paper

There are 18 elements in the 5th period of the modern periodic table. The 5th period consists of 18 elements. It begins with Rubidium (Z = 37) with filling of 5s-orbital and ends at Xenon (Z = 54) with the filling up of the 5p-orbitals. This period also contains 10 elements of 4d transition series starting at Yttrium (Z = 39).