- A $\rightarrow$ At (Nuclear number)
- $Z \rightarrow$ At #
- $Z$ \# protors $M_p$
- $(A-z)$ \# nentrons $M_n$
![image](https://temp-public-img-folder.s3.ap-south-1.amazonaws.com/sathee.prutor.images/subject-images/iitpal/image/Physics-Class-12-Unit-13-Chapter-02-The-Atomic-Nucleus-Masses-and-Stability-I-L-2_5-bij7Ibo9gsg-12.jpg)