How many transition series of elements are there in the periodic table.

Explanation

There are four main series of transition elements corresponding to the filling of 3d, 4d, 5d and 6d sublevels in 4th, 5th, 6th and 7th periods. The four series are known as first transition series or 3d series, second transition or 4d series, third transition or 5d series and fourth transition or 6d series.