A radioactive element `A` disintegrates in the following manner:
`A overset(- a)rarr B overset(-beta)rarr C overset(-beta) 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 distintegration:
`._(Z)A^(M) overset(- alpha)rarr ._(Z - 2)B^(M) overset(- beta)rarr ._(Z - 1)C^(M - 4) overset(- beta)rarr ._(Z)D^(M - 4)`
`A` and `D` are isotopes as both have same value of `Z`. `B,C` and `D` are isobars as these have same values of atomic mass.