Question

An element $E$ loses one $\alpha$ and two $\beta$ particles in three successive stages. The resulting element will be:

• A. an isobar of $E$
• B. an isotones of $E$
• C. an isotope of $E$
• D. $E$ itself

Answer 1

The correct option is C an isotope of $E$

An element $E$ loses one $\alpha$ and two $\beta$ particles in three successive stages. The resulting element will be an isotope of $E$.
When an alpha particle is lost, the atomic number decreases by 2 and the mass number decreases by 4. When a beta particle is lost, the atomic number increases by 1 but the mass number remains unchanged. Hence, when one alpha and two beta particles are successively lost, the atomic number remains same but the mass number decreases by 4. Hence, the daughter nucleus will be an isotope of the parent nucleus.

For example, ${}_{92}{U}^{238}$ and ${}_{92}{U}^{234}$ are isotopes.

${}_{92}{U}^{238}{\stackrel{-\alpha }{\to }}_{90}T{h}^{234}{\stackrel{-\beta }{\to }}_{91}P{a}_{234}{\stackrel{-\beta }{\to }}_{92}{U}^{234}$