In a radioactive decay chain reaction, 90230Th nucleus decays into...

Let number of $\alpha$ particles are ${n}_{\alpha}$ and $\beta$ particles are ${n}_{\beta}$.

Given: $90{Th}^{230}{\to}_{84}{Po}^{214} + {n}_{\alpha}\alpha + {n}_{\beta}\beta$.

Change in mass number is $= 230 - 214 = 4{n}_{\alpha}$

$⇒ {n}_{\alpha} = 4$

Number of proton, ${n}_{\beta} = 84 - \left(90 - 2{n}_{a}\right)$

$⇒ {n}_{\beta} = 2$

So, the ratio, $\dfrac{{n}_{\alpha}}{{n}_{\beta}} = 2$