Rearrange the column 2 and 3 so as to match with the column 1.Column 1Column 2Column 3(1) TriadConcentrated mass and +ve chargeThomson(2) OctaveAverage of the atomic masses of first and third elementNewlands Properties of the eighth element are simil…

Answer: (1) Triad – Average of the atomic masses of first and third element – Dobereiner; (2) Octave – Properties of the eighth element are similar to the first – Newlands.

Dobereiner arranged elements in groups of three (triads) with similar properties and showed that the atomic mass of the middle element is nearly the average of the atomic masses of the first and the third.

Newlands arranged the elements in increasing order of atomic mass and found that the properties of every eighth element are similar to those of the first, which he called the law of octaves.

The remaining pair, “concentrated mass and positive charge – Thomson”, belongs to the model of the atom, not to a periodic classification; the paper leaves the third entry of column 1 blank.