Answer:
The answer to your question is 18 neutrons
Explanation:
Data
Number of neutrons = ?
Atomic mass = 35
Three energy levels
seven valence electrons
Process
1.- We know that this element is on the third period (3 energy levels)
2.- We also know that this element is located on group 7A (it is a halogen)
3.- From the previous information, we conclude that this element is Chlorine.
4.- Chlorine has an atomic number of 17.
5.- The number of Neutrons = Atomic mass - atomic number
= 35 - 17
= 18
