The catalytic activity of transition metals is due to:

1.	High enthalpy of atomization
2.	Paramagnetic behaviour
3.	Colour of hydrated ions
4.	Variable oxidation states

The basic character of the transition metal monoxides follows the order:
(Atomic nos. Ti = 22, V = 23, Cr = 24, Fe = 26)

The correct order of ionic radii of Y³⁺, La³⁺, Eu³⁺, and Lu³⁺ is:

(Atomic nos. Y = 39, La = 57, Eu = 63, Lu = 71)

1. Y³⁺ < La³⁺ < Eu³⁺ < Lu³⁺

2. Y³⁺ < Lu³⁺ < Eu³⁺ < La³⁺

3. Lu³⁺ < Eu³⁺ < La³⁺ < Y³⁺

4. La³⁺ < Eu³⁺ < Lu³⁺ < Y³⁺

Mn²⁺ compounds are more stable than Fe²⁺ compounds towards oxidation in their +3 state because :

The +2 oxidation state becomes more stable in the first half of the first-row transition elements with increasing atomic number because:

The oxo metal anions of the 3d series in which the metal exhibits an oxidation state equal to its group number is /are:

The consequence(s) of lanthanoid contraction is/are :  

Which d-block elements are not considered transition elements, and why?

The different oxidation states exhibited by the lanthanoids are: