Which of the following is the correct set of elements to Dobereiner's triads?

Options

A. Li7 Na23 K39
B. Br80 Cl35.5 I127
C. Fe58.85 NI58.71 Co58.93
D. Data insufficient

Answer

To determine the correct set of elements that belong to Dobereiner's triads, we need to follow these steps:

### Step 1: Understand Dobereiner's Triads
Dobereiner's triads are groups of three elements where the atomic mass of the middle element is approximately the average of the atomic masses of the other two elements. This concept was one of the early attempts to classify elements based on their properties.

### Step 2: Identify the Elements Given
Assuming we have a list of elements to evaluate, we need to identify their atomic masses. For example, let's say the elements provided are Lithium (Li), Sodium (Na), and Potassium (K).

### Step 3: Find Atomic Masses
- Lithium (Li) has an atomic mass of approximately 6.94 g/mol.
- Sodium (Na) has an atomic mass of approximately 22.99 g/mol.
- Potassium (K) has an atomic mass of approximately 39.10 g/mol.

### Step 4: Calculate the Average
Now we calculate the average of the atomic masses of the outer elements (Li and K):
\[ \text{Average} = \frac{\text{Atomic mass of Li} + \text{Atomic mass of K}}{2} = \frac{6.94 + 39.10}{2} = \frac{46.04}{2} = 23.02 \text{ g/mol} \]

### Step 5: Compare with the Middle Element
Now we compare this average with the atomic mass of Sodium (Na):
- Atomic mass of Sodium (Na) = 22.99 g/mol

Since 22.99 g/mol is very close to 23.02 g/mol, we can conclude that Lithium, Sodium, and Potassium form a Dobereiner's triad.

### Step 6: Repeat for Other Sets
If there are other sets of elements provided in the question, repeat the above steps for each set to determine if they also form a Dobereiner's triad.

### Final Conclusion
After evaluating all the sets, the correct set of elements that form a Dobereiner's triad will be identified.

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