Atomic StructureHard
Question
Let Mp be the mass of photon, mn the mass of neutron. M1 the mass of 
necleus and M2 the mass of 
nucleus. Then
necleus and M2 the mass of nucleus. Then Options
A.M2 = 2M1
B.M2 > 2M1
C.M2 < 2M1
D.M1 < 10(mp + nn)
Solution
Due to mass defect (which is finally responsible for the binding energy of the nucleus), mass of the nucleus is always less than the sum of masses of its constituent particles.
is made up 10 protons plus 10 neutrons. Therefore mass of nucleus,
M1 < 10 (mp + mn)
Also, heavier the nucleus, more is the mass defect
Thus, 20 (mp + mn) - M2 > 10 (mp + mn) - M1
or 10(mp + mn) > M2 - M1
or M2 < M1 + 10 (mp + mn)
Now since, M1 < 10 (mp + mn)
∴ M2 < 2M1
is made up 10 protons plus 10 neutrons. Therefore mass of nucleus, M1 < 10 (mp + mn)
Also, heavier the nucleus, more is the mass defect
Thus, 20 (mp + mn) - M2 > 10 (mp + mn) - M1
or 10(mp + mn) > M2 - M1
or M2 < M1 + 10 (mp + mn)
Now since, M1 < 10 (mp + mn)
∴ M2 < 2M1
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