Question

A radioactive nucleus undergoes a series of decay according to the scheme ${A ->[\alpha] A1}$ ${ ->[\beta] A2}$ ${ ->[\alpha] A3}$ ${ ->[\gamma] A4}$ If the mass number and atomic number of A are 180 and 72 respectively, these numbers of $A_4$ are

• A. 172, 69
• B. 177, 69
• C. 171, 69
• D. 172, 68

Answer 1

Answer: (A)

172, 69

Answer 2

Decrease in mass number due to two $a = 2 ? 4 = 8$ Decrease in charge number due to two $a = 4$ Increase in charge number due to one $? = 1$ Net decrease in charge number $= 4 - 1 = 3$ $?$ affects neither. $\therefore$ For $A_{4}, A = 180 - 8 = 172$ $Z = 72 - 3 = 69$