Thorium (90) formed from emission of $\alpha$-particle from uranium (92, group IIIB) has been placed in group IIIB.

Q. Let us consider emission of $\alpha$-particle from uranium nucleus:
${}_{92}{U}^{235}{\to }_2{He}^4\to$ ${}_{90}{Th}^{231}$
$e=92$ $e=0$ $e=90$
$p=92$ $p=2$ $p=90$
$n=143$ $n=2$ $n=141$
Shortage of two electrons in thorium is due to:

Q. For emission of $\alpha$-particle from uranium nucleus, shortage of two electrons in thorium is due to :
${}_{92}{U}^{235}{-}_{2}H{e}^4{\to }_{90}T{h}^{231}$

Q. $\underset{92}{238}U\left(IIIB\right)$ changes to $\underset{90}{284}Th$ by emission of $\alpha$-particle. Daughter element will be in:

Q. Assertion :Element formed by the successive emission of 1$\alpha$-particle and 2$\beta$-particles is placed in the same group as the parent element. Reason: $\alpha$-particle is ${[}_2^{4}He{]}^{2+}$ while $\beta$-particle is ${}_{-1}^{0}e$.