Question

In the case of thorium $(A=232$ and $Z=90)$, we obtain an isotope of lead $(A=208$ and $Z=82)$ after some radioactive disintegrations. The number of $\alpha$-and $\beta$-particles emitted are, respectively,

• A. 6,3
• B. 6,4
• C. 5,5
• D. 4,6

Answer 1

Answer: (B)

Decrease in mass number $=232-208=24$
Number of $\alpha$-particles emitted $=\frac{24}{4}=6$
Due to emission of 6 particles, decrease in charge number is $12$.
But actual decrease in charge number is $8$.
Clearly, $4\beta$-particles are emitted.