neet phase 2

Which of the following group of elements are triad 1. Na, Ne, k 2. Cl, Br, I 3. Li, Fe, Ni 4. C, N, O

Dobereiner arranged elements as 1. groups 2. periods 3. triads 4. All the above

Triads means 1. Small groups of Three elements 2. Small groups of Four elements 3. Small groups of Five elements 4. Small groups of Six elements

The first classification of elements is attempted by 1. Dobereiner 2. Mendeleff 3. Mosley 4. John A.R. Newlands