5f-level is successively filled up in:

Actinoids

The correct answer is option 3. Actinoids.

Actinoids (or Actinides) are a series of elements in the periodic table with atomic numbers 89 through 103. These elements are characterized by the filling of the 5f orbitals.

Electronic Configuration and the 5f Orbitals:

The f-orbitals are located in the inner electron shells and can hold up to 14 electrons. They are divided into different series, with the 4f and 5f series being most notable in terms of periodic table elements. The 5f orbitals are filled in the actinoid series. These orbitals start filling after the 6s and 4f orbitals have been filled. 

The actinoids are found in the f-block of the periodic table, which is between the s-block and d-block elements. They include: Actinium \((Ac)\) through Lawrencium \((Lr)\). Their electron configurations involve the progressive filling of the 5f orbitals, starting with thorium \((Th, Z=90)\) and continuing through to lawrencium \((Lr, Z=103)\).

Example of Filling:

Thorium \((Th, Z=90)\): Electron configuration: \([Rn] 6s^2 5f^1\)

Uranium \((U, Z=92)\): Electron configuration: \([Rn] 6s^2 5f^3 6d^1\)

Plutonium \((Pu, Z=94)\): Electron configuration: \([Rn] 6s^2 5f^6 6d^1\)

The 5f orbitals are filled with electrons as you move across the series from thorium to lawrencium.

Other Elements:

1. Inert gases (Noble Gases): They belong to Group 18 and are characterized by completely filled s and p orbitals in their valence shell. They do not involve the \(5f\) orbitals.

2. Transition Elements: These elements are found in the d-block of the periodic table. Their electron configurations involve filling d orbitals, not \(f\) orbitals.

3. Lanthanides: They belong to the 4f series, where electrons are added to the \(4f\) orbitals. They are not related to the 5f orbitals which are specific to the actinoids.

Summary:

The 5f-level is successively filled in the actinoids. This series of elements is characterized by the filling of \(5f\) orbitals, which distinguishes them from other groups like raregases and transition elements, where the \(5f\) orbitals are not involved.