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

Answer

D

Explanation

`beta`-decay or `._(-1)e^(0)` decay leads to no change in mass number as `beta`-particle has zero mass.