In which of the following elements, 5f orbitals are progressively filled?

Options

A. Alkaline earth metals
B. Actinoids
C. Lanthanoids
D. Transition elements

Explanation

To determine which elements have progressively filled 5f orbitals, we need to understand the placement of these orbitals in the periodic table and the types of elements associated with them.

### Step-by-Step Solution:

1. **Identify the 5f Orbitals**: The 5f orbitals are part of the f-block of the periodic table. The f-block consists of two series: the lanthanides (4f) and the actinides (5f).

2. **Understand the Filling Order**: The filling of orbitals follows the Aufbau principle, which states that electrons occupy the lowest energy orbitals first. For the f-block, the 5f orbitals are filled after the 6s orbital.

3. **Locate the Actinides**: The actinides are the series of elements from actinium (Ac, atomic number 89) to lawrencium (Lr, atomic number 103). These elements progressively fill the 5f orbitals as you move from Ac to Lr.

4. **Evaluate the Options**:
- **Option 1: Alkaline Earth Metals** - These are group 2 elements and do not fill 5f orbitals.
- **Option 2: Actinides** - This is the correct option as these elements progressively fill the 5f orbitals.
- **Option 3: Lanthanides** - These elements fill the 4f orbitals, not the 5f.
- **Option 4: Transition Elements** - These elements fill the d orbitals, not the f orbitals.

5. **Conclusion**: The only series that progressively fills the 5f orbitals is the actinides.

### Final Answer:
**The elements in which the 5f orbitals are progressively filled are the actinides (Option 2).**