Question

A nucleus, with mass number $m$ and atomic number $n$, emits one $\alpha$ particle and one $\beta$ particle. The mass number and atomic number of the resulting nucleus will be respectively
(Assume $\beta$ is positron)

• A. $(m-2),n$
• B. $(m-4),(n-1)$
• C. $(m-4),(n-2)$
• D. $(m+4),(n-1)$

Answer 1

The correct option is B $(m-4),(n-1)$

An alpha particle is a doubly charged Helium ion.
$\alpha =H{e}^{2+}$
Mass no. of $\alpha$ = 4
Atomic no. of $\alpha$ = 2
$\beta$ particle
Mass no. of $\beta$ = 0
Change in atomic no. Atomic no. by $\beta$ = $\pm 1$
So
Resulting nucleus
Mass no. = $m-4$
Atomic No.=$n-1$ or $n-3$
(depending on whether $\beta =e^{+}./e^{-}$