Which are not anomalous pairs of elements in the Mendeleev’s periodic table?

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

To determine which pairs of elements are not anomalous in Mendeleev’s periodic table, we need to understand what "anomalous" means in this context. Anomalous pairs are those that do not fit the expected trends in properties based on their positions in the periodic table. Mendeleev arranged elements by increasing atomic mass, and sometimes this led to exceptions in the expected order of properties. Let's analyze each pair you've mentioned.

Analyzing the Element Pairs

1. Argon (Ar) and Potassium (K)

Argon is a noble gas, while potassium is an alkali metal. Their properties are quite different due to their positions in the periodic table. However, they are not considered anomalous because they belong to different groups and their properties align with their respective groups.

2. Cobalt (Co) and Nickel (Ni)

Cobalt and nickel are both transition metals and are located close to each other in the periodic table. They exhibit similar chemical properties, such as forming similar types of compounds. This pair is not anomalous as their properties are consistent with their positions.

3. Tellurium (Te) and Iodine (I)

Tellurium is a metalloid, while iodine is a halogen. Although they are adjacent in the periodic table, their properties differ significantly. This pair can be considered anomalous because their placement does not reflect a smooth transition in properties, particularly in terms of metallic character and reactivity.

4. Aluminum (Al) and Silicon (Si)

Both aluminum and silicon are in the same period and exhibit properties that are consistent with their positions. Aluminum is a metal, while silicon is a metalloid, but they share some similarities in terms of their chemical behavior, especially in forming compounds. Thus, this pair is not anomalous.

Conclusion of Analysis

From this analysis, we can conclude that the pairs that are not anomalous are:

• Argon (Ar) and Potassium (K)
• Cobalt (Co) and Nickel (Ni)
• Aluminum (Al) and Silicon (Si)

However, the pair that stands out as anomalous is Tellurium (Te) and Iodine (I). Therefore, the answer to your question is that the pairs that are not anomalous are A, B, and D.