The most abundant transition metal belongs to which of the following?

3d series

The most abundant transition metal belongs to the 3d series. The 3d series contains the elements scandium (Sc), titanium (Ti), vanadium (V), chromium (Cr), manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), and copper (Cu). These elements are the most abundant transition metals because they are found in the Earth's crust in relatively high concentrations.

The 4d series, 5d series, and 6d series contain fewer transition metals, and they are less abundant in the Earth's crust.

Here is a table of the abundance of the transition metals in the Earth's crust:

As you can see, the most abundant transition metal is iron, which belongs to the 3d series.