Question

An element $X$ decays into element $Z$ by two-step process.
$X⟶Y{+}_2^{4}He$
$Y⟶Z+2\overline{e}$ then

• A. $X$ and $Z$ are isobars
• B. $X$ and $Y$ are isotopes
• C. $X$ and $Z$ are isotones
• D. $X$ and $Z$ are isotopes

Answer 1

The correct option is D $X$ and $Z$ are isotopes

Let atomic number and mass number of $X$ be $Z$ and $A$, respectively.

First step of reaction : ${}_Z^{A}X{\to }_{Z-2}^{A-4}Y{+}_2^{4}He$

Second step of reaction : ${}_{Z-2}^{A-4}Y{\to }_Z^{A-4}Z+2$ ${}_{-1}^{0}e$

Atoms of elements having same atomic number and different mass number are known as isotopes.

Thus $X$ and $Z$ are isotopes.