Question

When a nucleus with atomic number $Z$ and mass number $A$ undergoes a radioactive decay process,

$\left(1\right)$ Both $Z$ and $A$ will decrease, if the process is $\alpha$ decay.
$\left(2\right)$ $Z$ will decrease, but $A$ will not change, if the process is ${\beta }^{+}$ decay.
$\left(3\right)$ $Z$ will increase, but $A$ will not change, if the process is ${\beta }^{-}$ decay.
$\left(4\right)$ $Z$ and $A$ will remain unchanged, if the process is $\gamma$ decay.

• A. $1$ & $2$ are true
• B. $1$,$2$ & $3$ are true
• C. All are true
• D. $3$ & $4$ are true

Answer 1

The correct option is C All are true

$\alpha$ decay is characterized by emission of $\alpha$ particle ${(}_2{\text{He}}^4)$. So, $A$ decreases by $4$ and $Z$ decreases by $2$.

${\beta }^{+}$ decay is characterized by emission of positron, when a proton inside the nucleus converts into neutron. So, $A$ remains the same and $Z$ decreases by $1$.

${\beta }^{-}$ decay is characterized by emission of electron, when a neutron inside the nucleus converts into proton.
So, $A$ remains the same and $Z$ increases by $1$.

When a radioactive decay occurs, the daughter nuclei might form in its excited state, and when it jumps to ground state, $\gamma$ radiations are emitted. This is called $\gamma$ decay. So, there will be no change in $Z$ and $A$.

Therefore, all the four statements are true.

Hence, option $\left(D\right)$ is correct.

Why this Question ? To know the basic definition about $\alpha ,{\beta }^{-},\gamma \text{and}{\beta }^{+}$decay.