In the disintegration of a radioactive element, `alpha`- and `beta`-particles are evolved from the nucleus.
`._(0)n^(1) rarr ._(1)H^(1) + ._(-1)e^(0) +` Antineutrino + Energy
`4 ._(1)H^(1) rarr ._(2)He^(4) + 2 ._(+1)e^(0) +` Energy
Then, emission of these particles changes the nuclear configuration and results into a daughter nuclide. Emission of an `alpha`-particles results into a daughter element having atomic number lowered by 2 and mass number by 4, on the other hand, emission of a `beta`-particle yields an element having atomic number raised by 1.
During `beta`-decay, the mass of atomic nucleus

Options

A. Decreases by 1 unit
B. Increases by 1 unit
C. Decreases by 2 units
D. Remains unaffected

Explanation

To solve the question regarding the mass of the atomic nucleus during beta decay, let's break it down step by step:

### Step 1: Understanding Beta Decay
Beta decay is a type of radioactive decay in which a beta particle (which is essentially an electron) is emitted from the nucleus of an atom. This process occurs when a neutron in the nucleus is transformed into a proton, resulting in the emission of a beta particle and an antineutrino.

### Step 2: Analyzing the Changes in Atomic Structure
When beta decay occurs, the following changes happen:
- A neutron is converted into a proton.
- The atomic number (Z) of the element increases by 1 because there is one more proton in the nucleus.
- The mass number (A), which is the total number of protons and neutrons, remains unchanged because the total number of nucleons (protons + neutrons) does not change.

### Step 3: Conclusion on Mass Change
Since the mass number remains the same during beta decay, we conclude that the mass of the atomic nucleus is unaffected by the emission of the beta particle.

### Final Answer
Thus, during beta decay, the mass of the atomic nucleus remains unaffected.