Question

Chlorine has atomic number 17 and mass number 35 it has?

Answer 1

Chlorine is atomic number 17 and it's atomic mass is 35.453 AMU

Answer 2

correct, the mass number is exactly 35.453 but of course it can be rounded to 35 for simplicity! hope that helps! if you would like an explanation on why, I'm happy to give it too :)