The atomic masses of Li and K are 7 and 39, respectively . According to law of triads the atomic mass of Na will be

Options

A. 23
B. 32
C. 46
D. 64

Answer

To find the atomic mass of sodium (Na) using the law of triads, we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Atomic Masses**:
- The atomic mass of Lithium (Li) is given as 7.
- The atomic mass of Potassium (K) is given as 39.

2. **Understand the Law of Triads**:
- According to the law of triads, when three elements are arranged in order of increasing atomic mass, the atomic mass of the middle element (in this case, Sodium) is equal to the average of the atomic masses of the first and third elements.

3. **Set Up the Equation**:
- Let the atomic mass of Sodium (Na) be represented as \( x \).
- According to the law of triads, we have:
\[ x = \frac{\text{Atomic mass of Li} + \text{Atomic mass of K}}{2} \]

4. **Substitute the Values**:
- Substitute the known values into the equation:
\[ x = \frac{7 + 39}{2} \]

5. **Calculate the Sum**:
- Calculate the sum of the atomic masses:
\[ 7 + 39 = 46 \]

6. **Calculate the Average**:
- Now, divide the sum by 2 to find the atomic mass of Sodium:
\[ x = \frac{46}{2} = 23 \]

7. **Conclusion**:
- Therefore, the atomic mass of Sodium (Na) is 23.

### Final Answer:
The atomic mass of Na is **23**.

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