After the emission of a $\beta$-particle followed by an $\alpha$-particle from ${ }_{83}^{214} \mathrm{Bi}$, the number of neurons in the atom is

• A

  210
• Correct answer
  B

  128
• C

  129
• D

  82

Solution

No. of neutrons $=$ Mass No. $(A)-$ Atomic No. $(Z)=210-82=128$

Hence, the correct answer is option: 'B'.