The answer to each of the following questions is a single digit integer ranging from 0 to 9. It the correct answers to the questions numbers A, B, C and S (say ) are 4, 0,9 and 2 respectively thent the correct darkening of bubbles should be us shown on the side :
How many series of elements constitute f- block elements

Explanation

To determine how many series of elements constitute the f-block elements, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding the f-block Elements**: The f-block elements are those that fill the f-orbitals. They are typically found at the bottom of the periodic table and consist of two series: the lanthanides and the actinides.

2. **Identifying the Series**:
- The **lanthanides** series includes elements with atomic numbers from 57 (lanthanum) to 71 (lutetium). This series contains a total of 15 elements.
- The **actinides** series includes elements with atomic numbers from 89 (actinium) to 103 (lawrencium). This series also contains 15 elements.

3. **Counting the Series**: Since we have identified two distinct series (lanthanides and actinides) that make up the f-block elements, we can conclude that there are two series.

4. **Final Answer**: Therefore, the number of series of elements that constitute the f-block elements is **2**.