Question

A radio nucleus produced due to ɑ-decay of the nucleus ${{}_Z{X^A}}$ is?
A. ${{}_{Z + 2}{Y^{A + 4}}}$
B. ${{}_Z{Y^A}}$
C. ${{}_{Z - 2}{Y^{A - 4}}}$
D. ${{}_{Z - 4}{Y^{A - 2}}}$

Answer 1

Hint:In a radioactive decay, the composition of the element changes according to the particles given out by it. Its composition changes because its mass number as well as the atomic number changes with every emission until it completely disappears. As the mass number is unique to every element, it gets converted to a new element altogether.



Complete answer:
The atomic number and mass number of alpha particles is 2 and 4, respectively. Also the mass number as well as atomic number must be conserved in a nuclear reaction.
When an alpha particle is emitted, its atomic number decreases by 2 and mass number decreases by 4. When a beta particle is emitted, its atomic number can increase or decrease by 1 depending upon the kind of beta particle emission. There is no change in the mass or charge when gamma particles are emitted. Therefore, when ${{}_Z{X^A}}$ emits alpha particles.
Thus the nuclear reaction is ${{}_Z{X^A} \to {}_{Z - 2}{Y^{A - 4}} + {}_2H{e^4}}$
Hence the atomic number of Y is Z-2.
The mass number of Y is A-4.
So, the radio nucleus produced a decay of ${{}_{Z - 2}{Y^{A - 4}}}$
Hence option C is the correct option
Additional information In the above reaction, an alpha particle is emitted from a nucleus ${{}_Z{X^A}}$. Hence this reaction is particularly known as alpha decay.



Note:The mass number is the sum of the number of protons and neutrons in an atom. The atomic number is the total number of protons present in the nucleus of an atom. Alpha particles are helium like particles, while beta particles are electrons or positrons with very high energy. Gamma particles are electromagnetic radiation.