The outer electronic configuration of Gd:
( At. No. 64) 

1. 4f⁵ 5d⁴ 6s¹
2. 4f⁷ 5d¹ 6s²
3. 4f³ 5d⁵ 6s²
4. 4f⁴ 5d⁵ 6s¹

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 of the following exhibits only a +3 oxidation state?

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

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

Actinoids exhibit more oxidation states than lanthanoids. The main reason for this is:

The d-electron configurations of Cr²⁺, Mn²⁺, Fe²⁺ and Ni²⁺ and 3d⁴, 3d⁵, 3d⁶ and 3d⁸ respectively.
Which one of the following aqua complexes will exhibit the minimum paramagnetic behaviour? 
(At. No. Cr = 24, Mn = 25, Fe = 26, Ni = 28)

1. \(\left[\mathrm{Mn}\left(\mathrm{H}_2 \mathrm{O}\right)_6\right]^{2+}\)
2. \(\left[\mathrm{Fe}\left(\mathrm{H}_2 \mathrm{O}\right)_6\right]^{2+}\)
3. \(\left[\mathrm{Ni}\left(\mathrm{H}_2 \mathrm{O}\right)_6\right]^{2+}\)
4. \(\left[\mathrm{Cr}\left(\mathrm{H}_2 \mathrm{O}\right)_6\right]^{2+}\)

Which one of the following ions is the most stable in an aqueous solution? 
(At. No. Ti = 22, V = 23, Cr = 24, Mn = 25)

1. $C{r}^{3+}$

2. $V^{3+}$

3. $T{i}^{3+}$

4. $M{n}^{3+}$