The electronic configurations of Eu (Atomic no. 63), Gd (Atomic no. 64), and Tb (Atomic no. 65) are, respectively:
 

1. [Xe] 4f⁶ 5d¹ 6s², [Xe]4f⁷ 5d¹ 6s², and [Xe] 4f⁹ 6s²

2. [Xe] 4f⁶ 5d¹ 6s², [Xe] 4f⁷5d¹ 6s², and [Xe]4f⁸ 5d¹ 6s²

3. [Xe] 4f⁷ 6s², [Xe]4f⁷ 5d¹ 6s², and [Xe] 4f⁹ 6s²

4. [Xe] 4f⁷ 6s², (Xe]4f⁸ 6s², and [Xe]4f⁸ 5d¹ 6s²

SO₂ is passed through an acidified K₂Cr₂O₇ solution.
The correct statement among the following regarding the above experiment is:

1. The solution gets decolorized.

2. SO₂ gets reduced.

3. Green coloured Cr₂(SO₄)₃ gets formed.

4. The solution turns blue.

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. $\left[Xe\right]4 f^6 5d^{2}6s^2$

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?

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.