Question

A nucleus of ²³⁵U₉₂ disintegrates to ²⁰⁷Pb₈₂ in about a billion years by emitting 7 alpha particles and x beta particles, where x is 

A) 3 

B) 4 

C) 5 

D) 6 

E) 7

Answer 1

The correct option is: (B) 4 

Explanation:

The mass number has changed by 28, the atomic number has changed by 10. 7 alpha particles (⁴He₂)*7 equates to a loss of 28 for atomic mass and 14 for atomic number. If only the alpha particles were emitted, 4 protons would be missing. Those protons must have come from the conversion of neutrons into protons which would happen with the release of 4 beta particles.