Which is not anomalous pair of elements in the Medeleeves periodic table -

Options

A. Ar and K
B. Co and Ni
C. Te and I
D. Al and Si

Answer

To determine which pair of elements is not an anomalous pair in Mendeleev's periodic table, we need to understand what an anomalous pair is. An anomalous pair refers to a situation where elements are arranged in a way that does not follow the expected trend based on their atomic masses, specifically when a higher atomic mass element is placed before a lower atomic mass element to maintain similar chemical properties.

### Step-by-Step Solution:

1. **Understand the Concept of Anomalous Pairs**:
- Anomalous pairs occur when elements are arranged contrary to the trend of increasing atomic mass to ensure that elements with similar chemical properties are grouped together.

2. **Identify Examples of Anomalous Pairs**:
- In Mendeleev's periodic table, some known anomalous pairs include:
- Argon (Ar) and Potassium (K)
- Cobalt (Co) and Nickel (Ni)
- Tellurium (Te) and Iodine (I)
- In these cases, the element with a higher atomic mass is placed before the one with a lower atomic mass.

3. **Evaluate the Given Options**:
- We need to identify which pair does not exhibit this anomalous behavior.
- The pair Aluminum (Al) and Silicon (Si) does not show this anomalous behavior as they follow the expected trend of increasing atomic mass.

4. **Conclusion**:
- Therefore, the pair that is not an anomalous pair in Mendeleev's periodic table is Aluminum (Al) and Silicon (Si).

### Final Answer:
The pair that is not an anomalous pair of elements in Mendeleev's periodic table is Aluminum (Al) and Silicon (Si).