Question

Helium nucleus is composed of two protons and two neutrons. If the atomic mass is $4.00388$, how much energy is released when the nucleus is constituted?
(Mass of proton $=1.00757$, Mass of neutron $=1.00893$)

• A. $271MeV$
• B. $27.12MeV$
• C. $2710MeV$
• D. $2.71MeV$

Answer 1

Answer: (B)

$27.12MeV$

The mass defect $\Delta m$ is the difference between the expected mass and actual mass.
$\Delta m=2\times \text{( mass of proton)}+2\times \text{(mass of neutron)}-\text{mass of helium nucleus}$
$\Delta m=2\times \text{1.00757}+2\times \text{1.00893}-\text{4.00388}$
$\Delta m=0.029116$ amu
1 amu $=931.5$ MeV
The amount of energy released when the nucleus is constituted $=\Delta m\times 931.5=0.029116\times 931.5=27.12$MeV