Gadolinium belongs to 4f series. It’s atomic number is 64. Which of the following is the correct electronic configuration of gadolinium?
1. \(\text{ [Xe] } 4f^8 6 d^2\)
2. \(\text { [Xe]}4 f^9 5 s^1\)
3. \(\text { [Xe] } 4f^7 5 d^1 6 s^2\)
4. \(\text { [Xe]} 4f^6 5 d^2 6 s^2\)

Assuming complete ionization, same moles of which of the following compounds will require the least amount of acidified KMnO₄ for complex oxidation?

1. $FeS{O}_4$

2. $FeS{O}_3$

3. $Fe{C}_2{O}_4$

4. $Fe{\left(N{O}_2\right)}_2$

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

(Numbers in the parenthesis are atomic numbers).

Which of the following processes does not involve the oxidation of iron?

The pair of compounds that can exist together is:

1. FeCl₃, SnCl₂

2. HgCl₂, SnCl₂

3. FeCl₂, SnCl₂

4. FeCl₃, Kl

In acidic medium, H₂O₂ changes Cr₂O₇^–2 to CrO₅ which has two (–O – O–) bonds.
The oxidation state of Cr in CrO₅ is:

1. +5

2. +3

3. +6

4. -10

The reason for the lanthanoid contraction is:

1. negligible screening effect of 'f' orbitals.

2. increasing nuclear charge.

3. decreasing nuclear charge.

4. decreasing screening effect.