Question

The radioactive decay of thorium $(A=232,Z=90)$ releases six alpha and four beta particles. The atomic number and mass number of the final product is

• A. $Z=80,A=207$
• B. $Z=82,A=208$
• C. $Z=92,A=209$
• D. $Z=90,A=207$

Answer 1

Answer: (B)

Decrease in mass number due to
$6\alpha =6\times 4=24$
Decrease in change number due to
$6\alpha =6\times 2=12$
Increase in change number due to four $\beta =4$
$\therefore$ Net mass number $=232-24=208$
Net atomic number $=90-12+4=82$