Question

What kind of radioactive decay does not lead to the formation of a daughter nucleus that is an isobar of the parent nucleus?
(A) $\alpha$ ray
(B) $\beta$ ray
(C) Positron
(D) Electron capture

Answer 1

The mechanism through which an unstable atomic nucleus releases energy by radiation is known as radioactive decay (also known as nuclear decay, radioactivity, radioactive disintegration, or nuclear disintegration). The term "radioactive" refers to a substance that contains reactive nuclei. Alpha decay, beta decay, and gamma decay are three of the most common methods of decay, all of which require the emission of one or more particles or photons. Beta decay is dominated by the weak force, while the other two are governed by the electromagnetic and strong forces, respectively.

Complete answer:
Alpha decay, also known as -decay, is a method of nuclear decay in which an atomic nucleus emits an alpha particle (helium nucleus) and thereby converts or 'decays' into a new atomic nucleus with a mass number of four and an atomic number of two.
$_{88}^{226}{\text{Ra}}\quad \to \quad _{86}^{222}{\text{Rn}} + _2^4{\text{He}} + 4.78{\text{MeV}}$
In nuclear physics, beta decay (-decay) is a type of radioactive decay in which an atomic nucleus emits a beta particle (fast energetic electron or positron) that transforms the initial nuclide into an isobar of that nuclide.
$_6^{44}{\text{C}} \to _7^{14}\;{\text{N}}{ + _{ - 1}}^0{\text{e}}$
Electron capture is a form of beta decay in which an electron is 'captured' by the atomic nucleus, usually from an inner (low-energy) orbital. The electron collides with one of the radioactive protons, resulting in the formation of a neutron and the emission of a neutrino. It's possible that the daughter nucleus is excited.
$_{19}^{40}\;{\text{K}} + _{ - 1}^0{\text{e}} \to _{18}^{40}{\text{Ar}}$
Positron emission, also known as beta plus decay, is a form of radioactive decay in which a proton within a radionuclide nucleus is converted to a neutron while simultaneously emitting a positron and an electron neutrino. The weak force is involved in positron emission.
$_Z^XA \to _1^0e + _{z - 1}^XB$
When a radioactive material emits $\alpha$ -particle, the nuclide's atomic number drops by two units and its atomic mass drops by four units.
Hence option A is correct.

Note:
Very heavy elements such as uranium, thorium, and radium undergo alpha decay. They're known as parent nuclei, because they're inherently unstable. These elements are neutron-rich since their nuclei contain far more neutrons than protons, resulting in an excessively high proton-to-neutron ratio. Alpha decay is inevitable because of this richness. As a result, it emits two protons and two neutrons as an alpha particle and becomes a new daughter nucleus, achieving a very stable structure.