A radioactive element `A` disintegrates in the following manner:
`A overset(- a)rarr B overset(-beta)rarr C overset(-beta)rarr D`
Which one (s) the elements `A, B, C`, and `D` are isotope (s) and which one (s) `is//are` isobar(s)?`

Explanation

Let the mass number and atomic number of element A be M and Z, respectively. The following changes shall occur during disintegration :
`._(Z)^(M)A overset(-alpha)(to) ._(Z - 2)^(M - 4)B overset(-beta)(to) ._(Z - 1)^(M - 4)C overset(-beta)(to) ._(Z)^(M - 4)D`
A and D are isotopes as both have same value of Z.
B,C and D are iosbars as these have same values of atomic.