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

Which one of the following statements is correct ?

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

Which one of the following elements will be an isobar of calcium if the atomic number of calcium is 20 and its mass number is 40?