Question

an atom of fluorine has the atomic number 9, and its mass number is 19. which of the following shows a neutral atom of fluorine?

Explanation:

Step1: Recall atomic - number and mass - number concepts

Atomic number = number of protons. For fluorine, atomic number = 9, so number of protons (p) = 9.

Step2: Calculate number of neutrons

Mass number = number of protons+number of neutrons. Given mass number = 19 and number of protons = 9, then number of neutrons (n)=mass number - number of protons = 19 - 9=10.

Step3: Recall neutral - atom concept

In a neutral atom, number of electrons = number of protons. Since number of protons = 9, number of electrons = 9.

Answer:

B. Y