Respuesta :

PunIntended

The mass number is the sum of the number of protons and number of neutrons the atom has.

So, we can write the equation as:

x + 20 = 40

x = 20 neutrons.

bossypants12345

Calcium's atomic number is 20, which means all calcium atoms have 20 protons in their nuclei. However, the number of neutrons in the nuclei of the calcium atoms can vary.

Hope this helps a little.