Whan a Dobereiner triad is considered, the sum
of atomic weights of extreme elements X and Z is
177.6 and difference of Z and Y is five times the
number of protons present in a neon atom. Identify
X, Y and Z.

Explanation

`x + y = 177xx6`
`z - y = 5 xx10`
`{:(177.6),(50.0),("____"),(127.6),("____"),():}`
`((-)(+) -)/(x + y= 127.6)`
As X, Y and Z from Dobereiner tried
`y = (x+ z)/(2)`, where x, y and z are atomic masses of
X, Y and Z, respectively
`y = (177.6)/(2) = 88.8`
`x = 127.6 - 88.8 = 38.8`
`z = 177.6 - 38.8 = 138.8`
`x = 38xx38 = 40`
`X = 40 rArr Ca`
` Y = 88xx80 rArr Sr`
`Z = 138xx6 rArr Ba ` .