Lanthanoid's most common oxidation state is:
1. 2
2. 5 
3. 3 
4. 4

Which of the following exhibits only a +3 oxidation state?

Four successive members of the first series of the transition metals are listed below. For which one of them does the standard potential $\left(E{°}_{M^{2+}/M}\right)$ value have a positive sign?
1.  Ni (Z = 28)
2.  Cu (Z = 29)
3.  Fe (Z = 26)
4.  Co (Z = 27)

Which one of the following does not correctly represent the correct order of the property indicated against it?

The catalytic activity of transition metals and their compounds is ascribed mainly to:

1. their unfilled d-orbitals
2. their ability to adopt variable oxidation states
3. their chemical reactivity
4. their magnetic behaviour

The aqueous solution containing which one of the following ions will be colourless:

1. Fe²⁺

2. Mn²⁺

3. Ti³⁺

4. Sc³⁺

[Atomic number : Sc = 21, Fe = 26, Ti = 24, Mn = 25]

Four successive members of the first-row transition elements are listed below with their atomic numbers. Which one of them is expected to have the highest third ionization enthalpy:

1. Vanadium (Z = 23)

2. Manganese (Z = 25)

3. Chromium (Z = 24)

4. Iron (Z = 26)

Colourless ion among the following is:

An element among the following that exhibits the maximum oxidation state is:

1. Cr

2. Mn

3. Fe

4. V

The main reason for a larger number of oxidation states exhibited by the actinoids than the corresponding lanthanoids is: