1 - An atom has a mass number of 24 and 13 neutrons. What is the atomic number of this atom?

2-Give the nuclear symbol for the isotope of argon for which A=38?

Enter the nuclear symbol for the isotope (e. g., 42He).

1. - The mass number of an atom equals the number of neutrons plus the number of protons. Then, for this atom the number of protons equals 24 less 13 = 11. The number of protons is the atomic number, so the answer is that the atomic number is 11.

2. - A = 38, means that the isotope of argon has mass number of 38. Given that the atomic number of argon is 18, this isotope has 18 protons and 38 less 18 = 20 neutrons. Then, the nuclear symbol is Ar precedeed by the numbers 38 (upper left corner) and 18 (lower left corner).