The given statement is true as explained below:

1.Atomic radii of the heavier transition elements (4d and 5d series) are larger than those of the corresponding elements of the first transition series through those of 4d and 5d series are very close to each other. (Lanthanoid contraction)

2. Due to stronger intermetallic bonding (M-M bonding), the melting and boiling points of heavier transition elements are greater than those of the first transition series.

3. The ionization enthalpies of 5d series are higher than the corresponding elements of 3d and 4d series.

4.The heavier transition elements form low spin complexes whereas the elements of the first series form low spin or high spin complexes depending upon the strength of ligand field.

Note: The strength of a ligand can be found out relating to its electronegativity. If a species is highly electronegative it has less tendency to donate e-s and thus is a weak field ligand and vice versa

5. +2 and +3 oxidation states are more common for elements in the first transition series, while higher oxidation states are more common for the heavier elements.