# Physics Class 12 NCERT Solutions: Chapter 13 Nuclei Part 9

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Q: 23. In a periodic table the average atomic mass of magnesium is given as. The average value is based on their relative natural abundance on earth. The three isotopes and their masses are,and The natural abundance of is by mass. Calculate the abundances of other two isotopes.

Answer:

Average atomic mass of magnesium,

Mass of magnesium isotope

Mass of magnesium isotope

Mass of magnesium isotope

Abundance of

Abundance of

Hence, abundance of

We have the relation for the average atomic mass as:

And

Hence, the abundance of is and that of is 11.71%.

Q: 24. The neutron separation energy is defined as the energy required to remove a neutron from the nucleus. Obtain the neutron separation energies of the nuclei and from the following data:

Answer:

For: Separation energy

ForSeparation energy

A neutron is removed from a nucleus. The corresponding nuclear reaction can be written as:

It is given that:

The mass defect of this reaction is given as:

Hence, the energy required for neutron removal is calculated as:

For , the neutron removal reaction can be written as:

It is given that:

The mass defect of this reaction is given as:

Hence, the energy required for neutron removal is calculated as: