Question

An atomic nucleus $A$ is composed of $84$ protons and $128$ neutrons.
$\left(i\right)$ The nucleus $A$ emits an alpha particle and is transformed into nucleus $B$. What is the composition of nucleus $B$?
$\left(ii\right)$ The nucleus $B$ emits a beta particle and is transformed into a nucleus $C$. What is the composition of nucleus $C$?
$\left(iii\right)$ Does the composition of nucleus $C$ change if it emits gamma radiations?

Answer 1

$\left(i\right)$ Given: Composition of atomic nucleus $A=84$ protons and $128$ neutrons.
Mass noumber of $A=84+128=212$
Atomic number of $A=84$
The nucleus $A$ emits an alpha particle, the mass number decreases by $4$ and the atomic number decreases by $2$.
${}_{84}^{212}A\underset{}{\overset{-\alpha }{\to }}{}_{82}^{208}B$
Number of protons in $B=82$
Number of neutrons in $B=208-82=126$

$\left(ii\right)$ ${}_{82}^{208}B\underset{}{\overset{-\beta }{\to }}{}_{83}^{208}C$
Number of protons in $C=83$
Number of neutrons in $C=208-83=125$

$\left(iii\right)$ The composition of nucleus $C$ does not change if it emits gamma radiations.