JEE Advanced 2019 · Paper 1 · Chemistry Q10

ChemistryMultiple correct+4 / -1Question 28 of 54

In the decay sequence,

$\ce{^{238}_{92}U ->[-x_1] ^{234}_{90}Th ->[-x_2] ^{234}_{91}Pa ->[-x_3] ^{234}\mathbf{Z} ->[-x_4] ^{230}_{90}Th}$

$x_1$ , $x_2$ , $x_3$ and $x_4$ are particles/radiation emitted by the respective isotopes. The correct option(s) is(are)

x_1

will deflect towards negatively charged plate

x_2

\beta^-

x_3

\gamma

-ray

Z is an isotope of uranium

Answer and worked solution

Official answer: A, B, D

The emissions.

$x_1$ : $\ce{^{238}_{92}U -> ^{234}_{90}Th}$ , so $x_1$ is an α particle. It is positive and deflects towards the negative plate. (A) is true.
$x_2$ : $\ce{Th(90) -> Pa(91)}$ at the same mass number, so $x_2$ is $\beta^-$ . (B) is true.
$x_3$ : $\ce{Pa(91) -> Z}$ at mass 234 can only be another $\beta^-$ , giving Z = 92. So $x_3$ is not a γ-ray, and (C) is false.
Z is $\ce{^{234}_{92}U}$ , an isotope of uranium. (D) is true. It then emits α ( $x_4$ ) to give $\ce{^{230}_{90}Th}$ .

(A), (B), (D)

Topics:Radioactive decay kinetics

JEE Advanced 2019 · Paper 1, Chemistry question 10