Question

Identify a Dobereiner’s triad from the first 20 element, other than Li, Na, K

Answer 1

There's no other triads  within the first 20 elements restriction Explanation: Only 3 known triads are there .

i)    Li(3), Na(11) , K(19)

ii)   Cl(17), Br (35) , I (53)

iii)  Ca(20) , Sr (38) , Ba(56)

As clearly seen , there's no other group of triads other than Li, Na, K that exsists within first 20 elements

Answer 2

There are no  Dobereiner’s triads within the first 20 elements of the periodic table except Li, Na, K.

• Dobereiner’s triads are a group of three elements in which the atomic mass of the middle element is the mean of the atomic masses of the other two elements.
• For example, the atomic mass of Na is 23 which is the mean of the atomic masses of Li(7) and K(39).
• There are only three known  Dobereiner’s triads out of which only Li, Na, K belongs to the first 20 elements of the periodic table.