To determine which of the given triads could not be justified as Doberiener's triad, we need to analyze each triad based on the principle that the atomic mass of the middle element should be approximately equal to the average of the atomic masses of the other two elements in the triad.
### Step-by-Step Solution:
1. **Understanding Doberiener's Triads**: Doberiener's triads consist of three elements where the atomic mass of the middle element is approximately the average of the atomic masses of the other two elements.
2. **Evaluate the Triads**:
- **Triad 1: Lithium (Li), Sodium (Na), Potassium (K)**
- Atomic masses: Li = 6.94, Na = 22.99, K = 39.10
- Average of Li and K: (6.94 + 39.10) / 2 = 23.02
- This is approximately equal to Na (22.99), so this triad is justified.
- **Triad 2: Chlorine (Cl), Bromine (Br), Iodine (I)**
- Atomic masses: Cl = 35.45, Br = 79.90, I = 126.90
- Average of Cl and I: (35.45 + 126.90) / 2 = 81.17
- This is approximately equal to Br (79.90), so this triad is justified.
- **Triad 3: Carbon (C), Nitrogen (N), Oxygen (O)**
- Atomic masses: C = 12.01, N = 14.01, O = 16.00
- Average of C and O: (12.01 + 16.00) / 2 = 14.00
- This is approximately equal to N (14.01), so this triad is justified.
- **Triad 4: Calcium (Ca), Strontium (Sr), Barium (Ba)**
- Atomic masses: Ca = 40.08, Sr = 87.62, Ba = 137.33
- Average of Ca and Ba: (40.08 + 137.33) / 2 = 88.71
- This is approximately equal to Sr (87.62), so this triad is justified.
3. **Conclusion**: After evaluating all the triads, all of them satisfy the criteria of Doberiener's triads. Therefore, none of the provided triads can be justified as not fitting into Doberiener's classification.
### Final Answer:
None of the given triads could be justified as not fitting into Doberiener's triad.
