How many anomalous pairs were present in original Mendeleev periodic table ?

Explanation

To determine how many anomalous pairs were present in the original Mendeleev periodic table, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Concept of Anomalous Pairs**:
An anomalous pair refers to a situation where elements with higher atomic weights are placed before elements with lower atomic weights in the periodic table. This placement is done to maintain similar chemical properties among the elements.

2. **Identify the Anomalous Pairs in Mendeleev's Table**:
In Mendeleev's periodic table, certain pairs of elements were identified as anomalous due to their placement based on chemical properties rather than strictly following atomic weight.

3. **List the Anomalous Pairs**:
The known anomalous pairs in Mendeleev's periodic table include:
- Argon (Ar) and Krypton (Kr)
- Cobalt (Co) and Nickel (Ni)
- Tellurium (Te) and Iodine (I)
- Thorium (Th) and Protactinium (Pa)

4. **Count the Anomalous Pairs**:
By listing the pairs, we can count them. There are a total of four anomalous pairs in the original Mendeleev periodic table.

### Final Answer:
There were **four anomalous pairs** present in the original Mendeleev periodic table.

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