Q. If M(A; Z), Mp and Mn denote the masses of the nucleus ᴬ_ZX, proton and neutron respectively in units of u (1 u = 931.5 MeV/c²) and BE represents its binding energy in MeV, then
A) M(A, Z) = ZMp + (A − Z)Mn + BE/c²
B) M(A, Z) = ZMp + (A − Z)Mn − BE/c²
C) M(A, Z) = ZMp + (A − Z)Mn + BE
D) M(A, Z) = ZMp + (A − Z)Mn − BE
Explanation
[Solution from source] A bound nucleus is lighter than its free nucleons by the mass defect, and the mass defect equals BE/c². So M(A, Z) = ZMp + (A − Z)Mn − BE/c². The plus sign would make the nucleus heavier than its parts, and subtracting BE without c² mixes energy with mass units. Answer (2).
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.