A pair among the following have nearly the same atomic radii:

(Numbers in the parenthesis are atomic numbers).

Gadolinium belongs to 4f series. It’s atomic number is 64. Which of the following is the correct electronic configuration of gadolinium?

1. $\left[Xe\right]4 f^8 6d^2$

2. $\left[Xe\right]4 f^9 5s^1$

3. $\left[Xe\right]4 f^7 5d^{1}6s^2$

4. $\left[Xe\right]4 f^6 5d^{2}6s^2$

Identify the incorrect statements related to lanthanons:
 

The electronic configuration of the last element of actinoids is :

1. Thorium, Th: $\left[\mathrm{Rn}\right]5{\mathrm{f}}^{14}6{\mathrm{d}}^{1}7{\mathrm{s}}^2$

2. Lawrencium, Lr: $\left[\mathrm{Rn}\right]5{\mathrm{f}}^{14}6{\mathrm{d}}^{1}7{\mathrm{s}}^2$

3. Neptunium, Np: $\left[\mathrm{Rn}\right]5{\mathrm{f}}^{14}6{\mathrm{d}}^{1}7{\mathrm{s}}^2$

4. Protactinium, Pa: $\left[\mathrm{Rn}\right]5{\mathrm{f}}^{14}6{\mathrm{d}}^{1}7{\mathrm{s}}^2$

The point of dissimilarity between lanthanides and actinides is: