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

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

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.