A nucleus ${^{238}_{92}X}$ emits one alpha particle and then one beta particle (electron). The product nucleus will have
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → Atomic number 91, Mass number = 234
Parent nucleus: $_{92}^{238}X$
After $\alpha$-decay: $\ ^4_2He$ is emitted
$\ ^{238}_{92}X \;\;\to\;\; ^{234}_{90}Y$
So, $A=234$, $Z=90$
Now $\beta^-$-decay: one electron is emitted
$\ ^{234}_{90}Y \;\;\to\;\; ^{234}_{91}Z$
So, $A=234$, $Z=91$
Final Answer: Atomic number = 91, Mass number = 234