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Read the passage given below and answer the following questions:
The f-block elements are those in which the differentiating electron enters the $(n -2)f$ orbital. There are two series of F-block elements corresponding to filling of $4f $ and $5f-$orbitals. The series of $4f-$orbitals is called lanthanides. Lanthanides show different oxidation states depending upon stability of $f^0, f^7$ and $F^{14}$ configurations, though the most conunon oxidation states is $+3$. There is a regular decrease in size oflanthanides ions with increase in atomic number which is known as lanthanide contraction.
The following questions are multiple choice questions. Choose the most appropriate answer:

1. The atomic numbers of three lanthanide elements $X, Y$ and $Z$ are $65, 68$ and $70$ respectively, their $Ln^{3+}$ electronic configuration is:

1. $4f^8, 4f^{11}, 4f^{13}$
2. $4f^{11}, 4f^8, 4f^{13}$
3. $4f^0, 4f^2, 4f^{11}$
4. $4f^3, 4f^7, 4f^9$

2. Lanthanide contraction is observed in:

1. $Gd$
2. $At$
3. $Xe$
4. $Te$

3. Which of the following is not the configuration oflanthanoid?

1. $[Xe]4f^{10}6s^2$
2. $[Xe]4f^15d^16s^2$
3. $[Xe]4d^{14}5d^{10}6s^2$
4. $[Xe]4f^75d^16s^2$

4. Name a member of the lanthanoid series which is well known to exhibit +4 oxidation state.

1. Cerium $(Z = 58)$
2. Europium $(Z = 63)$
3. Lanthanum $(Z = 57)$
4. Gadolinium $(Z = 64)$

5. Identify the incorrect statement among the following.

1. Lanthanoid contraction is the accumulation of successive shrinkages.
2. The different radii of $Zr$ and $Hf$ due to consequence of the lanthanoid contraction.
3. Shielding power of $4f$ electrons is quite weak.
4. There is a decrease in the radii of the atoms or ions as one proceeds from La to Lu.