The atomic masses of three elements X, Y and Z having similar chemical properties are 7, 23 … which can be classified according to…
(a) Average atomic mass = (Mass X + Mass of Z)/2 = (7 + 39)/2 = 23
(b) The average atomic mass of elements X and Z is equal to the atomic mass of element Y.
(c) Dobereiner’s law of triads.
(d) X is lithium, Y is sodium and Z is potassium.
(e) Chlorine, Bromine, Iodine.