Question

A nucleus ${}_{11}^{24}Na$ is β-radioactive. What are the numbers $24$ and $11$ called ?

• A. 24 - neutron number, 11 - atomic number
• B. 24 - electron number, 11 - atomic number
• C. 24 - mass number, 11 - atomic number
• D. 11 - mass number, 24 - atomic number

Answer 1

The correct option is C 24 - mass number, 11 - atomic number

Generally a nucleus is represented as ${}_Z^{A}X$ where $A=$ mass number and $Z=$ proton number or atomic number.

Here, mass number $A=24$ and atomic number, $Z=11$ and the neutron number, $N=A-Z=24-11=13$