Question

During $\beta^{-}$decay of a radioactive element there is an increase in its

• A. mass number
• B. neutron number
• C. electron number
• D. proton number
• E. atomic weight

Answer 1

Answer: (B)

When a $\beta^{-}$-particle is emitted by a nucleus, its atomic number $(z)$ is increases by one but mass number remains unchanged, i.e.
${} _Z X ^A \xrightarrow{\beta^- \text{partical}} {}_{Z+1}Y^A$ $+$ anti-neutrino $+e^{-}$
Since, $Z=$ number of protons $=$ number of electrons.