Which of the following triads was **not** given by Dobereiner?

Johann Wolfgang Döbereiner proposed the Law of Triads, where elements with similar chemical properties were grouped in threes such that the atomic mass of the middle element was approximately the arithmetic mean of the other two. His recognized triads included the alkali metal group (Li, Na, K), the alkaline earth metal group (Ca, Sr, Ba), and the halogen group (Cl, Br, I). While Nitrogen (N), Phosphorus (P), and Arsenic (As) are often discussed in the context of his work, historical records and textbooks confirm that Ca, Sr, Ba and Cl, Br, I were his primary successful triads. The combination of Beryllium (Be), Magnesium (Mg), and Calcium (Ca) was not one of Döbereiner's triads; although they belong to the same modern group, the arithmetic mean of Be (9) and Ca (40) is 24.5, which does not closely match Mg (24.3) in the specific historical context of his identified sets.