A radioactive nucleus decays as given below:
Which particles are emitted in the sequence?
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → \( \beta, \alpha, \gamma \)
Each kind of decay changes the atomic number \( Z \) and the mass number \( A \) in a fixed way: \( \alpha \) decay lowers \( Z \) by 2 and \( A \) by 4; \( \beta^{-} \) decay raises \( Z \) by 1 and leaves \( A \) unchanged; \( \gamma \) decay only releases energy from an excited nucleus (marked *), so \( Z \) and \( A \) do not change.
\( P \rightarrow Q:\ Z \rightarrow Z+1,\ A\ \text{unchanged} \;\Rightarrow\; \beta \)
\( Q \rightarrow R^{*}:\ Z+1 \rightarrow Z-1,\ A \rightarrow A-4 \;\Rightarrow\; \alpha \)
\( R^{*} \rightarrow R:\ \text{no change, excited state to ground state} \;\Rightarrow\; \gamma \)
So the particles are emitted in the order \( \beta, \alpha, \gamma \).
Note: A similar question was also asked in CUET (UG) 2025 on 30-05-2025 (Slot 2).