Mercury has an atomic number of 80 and a mass number of 200.

How many neutrons are in one atom of mercury?

a. 40

b. 80

c. 120

d. 200

Answer: The correct answer is Option c.

Explanation:

Atomic number is defined as the number of protons or electrons that are present in a neutral atom.

Atomic number = number of protons = number of electrons

Mass number is defined as the sum of number of protons and number of neutrons present in an atom.

Mass number = Number of neutrons + Number of protons.

We are given:

Atomic number = 80

Mass number = 200

Number of neutrons = Mass number - Atomic number = 200 - 80 = 120

Hence, the correct answer is Option c.

C. The mass number is the amount of Protons and electrons there are combined, so 200 - 80 is 120.