The atomic number of an element determines the number of protons in its nucleus. Since the atomic number of the element is 15, it has 15 protons.
The atomic mass of an element is the sum of the number of protons and neutrons. Given that the atomic mass is 31, we can calculate the number of neutrons using the following formula:
\[ \text{Neutrons} = \text{Atomic Mass} - \text{Protons} \]
Substituting the values:
\[ \text{Neutrons} = 31 - 15 = 16 \]
In a neutral atom, the number of electrons is equal to the number of protons. Therefore, this element also has 15 electrons.
To summarize:
- Number of protons: 15
- Number of neutrons: 16
- Number of electrons: 15