Question

the diagram below represents the nucleus of an atom. key: ● = proton ○ = neutron. what are the atomic number and mass number of this atom? the atomic number is 11 and the mass number is 19. the atomic number is 9 and the mass number is 20. the atomic number is 9 and the mass number is 19. the atomic number is 11 and the mass number is 20.

Explanation:

Step1: Count protons

The atomic number is equal to the number of protons. Counting the dark - colored (proton) circles in the nucleus diagram gives the atomic number.

Step2: Count neutrons and protons

The mass number is the sum of protons and neutrons. After counting protons and neutrons (light - colored circles) in the nucleus diagram, add them together to get the mass number.

Answer:

We need to count the protons and neutrons from the diagram. If we assume there are 9 protons and 10 neutrons:
The atomic number is 9 (number of protons) and the mass number is 9 + 10=19. So the answer is: The atomic number is 9 and the mass number is 19.