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Atoms and Nuclei question

2007 · Shift 0 · Q63
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Atoms and Nuclei question

2007 · Shift 0 · Q63

JEE MainPhysicsAtoms and NucleiMCQ+4 / −1
If MO{M_O}MO​ is the mass of an oxygen isotope 8O17{}_8{O^{17}}8​O17, Mp{M_p}Mp​ and MN{M_N}MN​ are the masses of a proton and neutron respectively, the nuclear binding energy of the isotope is
  1. A
    (MO−17MN)C2\left( {{M_O} - 17{M_N}} \right){C^2}(MO​−17MN​)C2
  2. B
    (MO−8MP)C2\left( {{M_O} - 8{M_P}} \right){C^2}(MO​−8MP​)C2
  3. C
    (MO−8MP−9MN)C2\left( {{M_O} - 8{M_P} - 9{M_N}} \right){C^2}(MO​−8MP​−9MN​)C2
  4. D
    MOc2{{M_O}{c^2}}MO​c2
View written solutionFree

Correct answer: $\BOXED{(8M_P + 9M_N - M_O)C^2}$

  1. Identify the nucleus composition

For the isotope 8O17{}_8O^{17}8​O17:

  • Atomic number Z=8Z = 8Z=8 ⇒\Rightarrow⇒ number of protons =8= 8=8
  • Mass number A=17A = 17A=17 ⇒\Rightarrow⇒ number of neutrons =17−8=9= 17 - 8 = 9=17−8=9

So the nucleus contains: 8 protons and 9 neutrons8\text{ protons and }9\text{ neutrons}8 protons and 9 neutrons

  1. Write the general expression for binding energy

Nuclear binding energy is given by: B.E.=(sum of masses of free nucleons−mass of nucleus)c2B.E. = (\text{sum of masses of free nucleons} - \text{mass of nucleus})c^2B.E.=(sum of masses of free nucleons−mass of nucleus)c2

Thus, B.E.=(8Mp+9MN−MO)c2B.E. = \left(8M_p + 9M_N - M_O\right)c^2B.E.=(8Mp​+9MN​−MO​)c2

  1. Compare with the given options
  • Option A: (MO−17MN)c2\left(M_O - 17M_N\right)c^2(MO​−17MN​)c2 This is incorrect because it does not include 8 protons separately.

  • Option B: (MO−8Mp)c2\left(M_O - 8M_p\right)c^2(MO​−8Mp​)c2 This ignores the 9 neutrons, so incorrect.

  • Option C: (MO−8Mp−9MN)c2\left(M_O - 8M_p - 9M_N\right)c^2(MO​−8Mp​−9MN​)c2 This is the negative of the standard expression. The correct physical binding energy should be: (8Mp+9MN−MO)c2\left(8M_p + 9M_N - M_O\right)c^2(8Mp​+9MN​−MO​)c2 So as written, this option has the wrong sign.

  • Option D: MOc2M_Oc^2MO​c2 This is just rest energy of the isotope, not binding energy.

  1. Conclusion

The correct expression for nuclear binding energy is: (8Mp+9MN−MO)c2\boxed{\left(8M_p + 9M_N - M_O\right)c^2}(8Mp​+9MN​−MO​)c2​

This does not match any option exactly. Option C has the correct masses involved but the sign is reversed.

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