Question

$\alpha$ and $\beta$ - particles emitted when uranium nucleus ${}_{92}{U}^{238}$ decay to ${}_{82}P{b}^{214}$ are

• A. 6 - $\alpha$ particles and 2- $\beta$ particles
• B. 4 $\alpha$ - particles and 2 $\beta$ particles
• C. 2- $\alpha$ particles and 6 $\beta$ particles
• D. 2 $\alpha$ -particles and 4 $\beta$-particles

Answer 1

Answer: (A)

6 - $\alpha$ particles and 2- $\beta$ particles

When an alpha particle is emitted from a radioactive substance its atomic number($Z$) decreases by $2$ and mass number($A$) decreases by $4$. When $\beta$ particle is emitted from a radioactive substance its atomic number(Z) increases by $1$ and mass number($A$) does not change.

Here, Uranium decays to lead its mass no changes to by $24$ i.e.

$\frac{24}{4}=6\alpha$ particles are emitted and hence, its atomic

number changes by 12 but the atomic numbre of $P_b$ is 10 this is due to emission of two $\beta$ particle.

${}_{92}^{238}\text{U}\to 6{\alpha }_2^4+2{\beta }_1^0{+}_{82}^{214}\text{Pb}$