Question

what is meant my dobernier traids

Answer 1

Dobereiner's law of triads states that,

The atomic weight of the middle element is equal to the average of atomic weights of other two elements.

Example,

Lithium (Li)
Sodium (Na)
Pottasium (K)

Atomic weights of

Li - 7
Na - 23
K - 39

Atomic weight of Na = average of atomic weights of Na and K

23 = (7+39)/2

23 = 46/2

23 = 23

So,both are equal.

Hope it helps..

Answer 2

Dobereiner's law of triads states that,

The atomic weight of the middle element is equal to the average of atomic weights of other two elements.

Example,

Lithium (Li) 
Sodium (Na)
Pottasium (K)

Atomic weights of 

Li - 7
Na - 23
K - 39

Atomic weight of Na = average of atomic weights of Na and K

23 = (7+39)/2

23 = 46/2

23 = 23

So,both are equal.