Question

Atom A has an atomic number of 19 and mass number of 40. Atom B has an atomic number of 20 and a mass number of 40. Which of these is an accurate statement?

A) Atom A has more protons than Atom B.
B) Atom A has one less proton and one more neutron than Atom B.
C) Atom A has an extra nucleon compared to Atom B.
D) Atom A has one more proton and one more electron than Atom B.

Answer 1

B) Atom A has one less proton and one more neutron than Atom B.

Step-by-step 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.

Answer 2

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.