Question

If $M$ is the atomic mass and $A$ is the mass number, packing fraction is given by :

• A. $\frac{M}{M-A}$
• B. $\frac{M-A}{A}$
• C. $\frac{A}{M-A}$
• D. $\frac{A-M}{A}$

Answer 1

The correct option is B $\frac{M-A}{A}$

Packing fraction is the ratio of number of neutrons to the number of protons. Since number of protons in an atom is $A$ and number of neutrons is $N=M-A$.

Hence, packing fraction is $\eta =\frac{N}{A}=\frac{M-A}{A}$