Read the information given below to answer
In \( \alpha \)-decay, the mass number of daughter nucleus is four less than that of decaying nucleus (parent nucleus). While atomic number decreases by two. In general, \( \alpha \)-decay of parent nucleus \( {}^{A}_{Z}X \) results in daughter nucleus \( {}^{A-4}_{Z-2}Y \)
\( {}^{A}_{Z}X \longrightarrow {}^{A-4}_{Z-2}Y + {}^{4}_{2}\mathrm{He} \)
From Einstein’s mass energy equivalence relation and energy conservation, it is clear that this spontaneous decay is possible only when mass of decay products is less than the mass of the parent nucleus. By referring the table of nuclear masses, one can check that the total mass of daughter nucleus and \( \alpha \)-particle is indeed less than that of parent nucleus.
The disintegration energy or the \( Q \) value can be calculated by formula \( Q = \Delta m \cdot c^{2} \)
\( \alpha \) particle is :
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → Nucleus of Helium atom
An \( \alpha \)-particle is \( {}^{4}_{2}\mathrm{He} \) with no electrons: two protons and two neutrons bound together, carrying a charge of \( +2e \). That is exactly the nucleus of a helium atom.
NCERT (2026-27):
Radioactivity – “… Three types of radioactive decay occur in nature : (i) α-decay in which a helium nucleus 42He is emitted; (ii) β-decay in which electrons or positrons (particles with the same mass as electrons, but with a charge exactly opposite to that of electron) are emitted; (iii) γ-decay in which high energy (hundreds of keV or more) photons are emitted.”