Which one of the following statements is not correct?

Which one of the following statements is correct ?

The mass number of argon is 40. Which one of the following statements is correct?

Which one of the following statements about the properties of neutrons is not correct?

For Aluminium (Al) (atomic number: 13, mass number: 27), which one among the following statements is NOT correct?

Which one of the following ions is not iso-electronic with F⁻ ?