Atomic wt. of Cl = 35.5 and of I = 127. According to doeberiner triad rule, At. wt. of Br will be

Options

A. `80.0`
B. 162.5
C. 81.25
D. 91.5

Answer

To find the atomic weight of Bromine (Br) using the Doberiner Triad rule, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Doberiner Triad Rule**:
- The Doberiner Triad rule states that when three elements with similar properties are arranged in a triad, the atomic weight of the middle element can be calculated as the average of the atomic weights of the other two elements.

2. **Identify the Elements**:
- In this case, the triad consists of Chlorine (Cl), Bromine (Br), and Iodine (I).
- Given atomic weights:
- Atomic weight of Cl = 35.5
- Atomic weight of I = 127

3. **Apply the Doberiner Triad Formula**:
- According to the rule, the atomic weight of Br can be calculated using the formula:
\[ \text{Atomic weight of Br} = \frac{\text{Atomic weight of Cl} + \text{Atomic weight of I}}{2} \]

4. **Substitute the Values**:
- Substitute the known atomic weights into the formula:
\[ \text{Atomic weight of Br} = \frac{35.5 + 127}{2} \]

5. **Calculate the Sum**:
- First, calculate the sum of the atomic weights:
\[ 35.5 + 127 = 162.5 \]

6. **Calculate the Average**:
- Now, divide the sum by 2 to find the atomic weight of Br:
\[ \text{Atomic weight of Br} = \frac{162.5}{2} = 81.25 \]

7. **Conclusion**:
- Therefore, the atomic weight of Bromine (Br) is 81.25.

### Final Answer:
The atomic weight of Br is **81.25**.

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