Question

Which of the following reactions is impossible?

• A. ${}_2{\text{He}}^4$ + ${}_4{\text{Be}}^9$ = ${}_0{\text{n}}^1$ +${}_6{\text{C}}^{12}$
• B. ${}_2{\text{He}}^4$ + ${}_7{\text{N}}^{14}$ = ${}_1{\text{H}}^1$ + ${}_8{\text{O}}^{17}$
• C. 4(${}_1{\text{H}}^1$) = ${}_2{\text{He}}^4$ + 2(${}_1{\text{e}}^0$)
• D. ${}_3{\text{Li}}^4$ + ${}_1{\text{H}}^1$ = ${}_4{\text{Be}}^8$

Answer 1

Answer: (D)

${}_3{\text{Li}}^4$ + ${}_1{\text{H}}^1$ = ${}_4{\text{Be}}^8$

In the nuclear reactions atomic mass of nucleons should remained conserved on either sides of reaction or mass of product nuclei should be less than the reacting ones.
A] In first reaction the total atomic mass of reactant nuclei i.e. $He$ and $Be(9+4=13)$ is equal to the mass of product nuclei i.e. C and neutron$(12+1=13).$
B] Also, in second reaction the total atomic mass of reactant nuclei i.e. $He$ and $N(4+14=18)$ is equal to the mass of product nuclei i.e. proton and oxygen$(1+17=18)$.
C] Similarly in third reaction mass is conserved between $4$ protons and alpha particle.
D] In this reaction, mass of lithium and proton is less than the isotope of $Be$ this is not possible since, the light nuclei combines to form the heavier one of equal mass or with some mass defect which is converted into energy. But in given reaction mass of product nucleus is large which is in contradiction.