Question

Successive emission of an $\alpha - $particle and two $\beta - $particles by an atom of a radioactive element results in the formation of its:
(A) Isobar
(B) Isomer
(C) Isotone
(D) Isotope

Answer 1

Hint: In alpha decay, release of a helium nucleus takes place that means the nuclei will observe a decrease in the total mass by 4 while the atomic number will be reduced by 2. However, beta decay is the decay of a neutron to a proton which releases an electron. Due to this, the mass of the atom remains the same but the atomic number is increased by 1.

Complete Step by Step Solution:
In order to become stable, the decay of a radioactive element takes place. Usually, a single decay is not enough for a radioactive nucleus to reach a stable state due to which it undergoes a series of decays until a stable nucleus is formed. There are three types of decays which are described as follows:
Alpha decay: It is a mode of radioactive decay in which a nucleus emits a helium nucleus i.e., two protons and two neutrons.
Beta decay: It is the mode of radioactive decay in which a nucleus emits a beta particle and a release of electrons takes place due to which the nucleus formed after decay has an atomic number higher by the value of 1.

For the given question, let us consider a radioactive element $X$ with atomic mass $A$ and atomic number $Z$. Thus, alpha and beta decay can be represented as follows:
$X_{Z}^{A}\xrightarrow{\alpha }X_{Z-2}^{A-4}\xrightarrow{\beta }X_{Z-1}^{A-4}\xrightarrow{\beta }X_{Z}^{A-4}$

Hence, on successive emissions, the atomic number remains the same but the change is observed in atomic mass. We know that atoms with different atomic mass but same atomic number are referred as isotopes. Therefore, formation isotope takes place after successive emissions.
So, option (D) is the correct answer.

Note: It is important to note that isobars are the atoms with the same atomic mass but different atomic number whereas isotones are the atoms which have the same number of neutrons while number of electrons and protons differ.