Mass number

A helium atom has 2 protons. It has an atomic mass of 4. How many neutrons does it have?

• 2

• 4

• 6

• 8

A phosphorus atom has 15 protons. It has a mass number of 31. How many neutrons does it have?

• 15

• 16

• 31

• 6

True or false: The mass number is the number of protons + the number of neutrons.

• True

• False

A sodium atom has 11 protons. It has a mass number of 23. How many neutrons does it have?

• 11

• 23

• 12

• 5

A berilium atom has 4 protons. It has a mass number of 9. How many neutrons does it have?

• 5

• 4

• 9

• 8

A mercury atom has 80 protons. It has a mass number of 201. How many neutrons does it have?

• 201

• 121

• 80

• 281

A calcium atom has 20 protons. It has a mass number of 40. How many neutrons does it have?

The atomic number of nitrogen is 7. Its mass number is 14. How many neutrons does it have?

• 7

• 48

• 14

• 4

If an element has 5 protons and 9 neutrons, what is its mass number?

• 14

• 5

• 9

• 2

If an element has 17 protons and 20 neutrons, what is its mass number?

• 17

• 10

• 20

• 37