Question

An element $A$ decays into element $C$ by the following two step processes:
$A⟶{{}_{2}He}^4+B$
$B⟶2\left({{}_{-1}e}^0\right)+C$
Select pair for isobars from elements $A,B$ and $C$.

Answer 1

Isobars are atoms with same mass number but different atomic number.

Let atomic number of $A$ be $Z$

Let mass number of $A$ be $X$

$A{⟶}_{2}H{e}^4+B$

Therefore, Atomic number of $B$ will be $Z-2$

Mass number of $B$ will be $Z-4$

$B⟶2{(}_{-1}{e}^0)+C$

Therefore, Atomic number of $C$ will be $Z$

Mass number of $C$ will be $Z-4$

It can be seen that $B$ and $C$ have same mass number but different atomic number. Hence, $B$ and $C$ are isobars.