In the nuclear decay given below, the particles emitted in the sequen…

The correct answer is Option (4) → \( \beta, \alpha, \gamma \)

Each kind of decay changes the mass number \( A \) and the atomic number \( Z \) in its own way: alpha decay lowers \( A \) by 4 and \( Z \) by 2, beta-minus decay keeps \( A \) and raises \( Z \) by 1, and gamma decay changes neither, it only takes an excited nucleus (marked *) down to a lower energy state.

P to Q: \( A \) is unchanged and \( Z \) rises from \( Z \) to \( Z+1 \), so a \( \beta^{-} \) particle is emitted.

Q to R*: \( A \) falls by 4 and \( Z \) falls from \( Z+1 \) to \( Z-1 \), that is by 2, so an \( \alpha \) particle is emitted.

R* to R: \( A \) and \( Z \) stay the same; the excited nucleus drops to its ground state, so a \( \gamma \) ray is emitted.

So the sequence is \( \beta, \alpha, \gamma \).

Note: A similar question was also asked in CUET (UG) 2023 on 30-05-2023 (Slot 1).

NCERT (2026-27):
Radioactivity – “… Experiments performed subsequently showed that radioactivity was a nuclear phenomenon in which an unstable nucleus undergoes a decay. This is referred to as radioactive decay. Three types of radioactive decay occur in nature :

(i) α-decay in which a helium nucleus ⁴₂He is emitted;

(ii) β-decay in which electrons or positrons (particles with the same mass as electrons, but with a charge exactly opposite to that of electron) are emitted;

(iii) γ-decay in which high energy (hundreds of keV or more) photons are emitted.”