Respuesta :
First, the atomic number is equal to the number of protons. Also, the mass number is protons plus neutrons, as electrons weigh so little that they are not included. So Atom A has 19 protrons and 21 neutrons, while Atom B has 20 protons and 20 neutrons.
Answer A and B are not true because Atom A has 1 less proton than Atom B. Answer C is not correct because nucleons are either protons or neutrons, which both atoms have an equal number of, as they have a mass of 40. Therefore, the answer must be B.
Answer:
B) Atom A has one less proton and one more neutron than Atom B.
Explanation:
Atom A has the same mass but one less proton. So, Atom A has one less proton and one more neutron than Atom B.