The table below shows the number of sub-atomic particles in an atom of magnesium. Sub-atomic Particles Sub-atomic Particle

Protons 12

Neutrons 12

Electrons 12

What is the amu of a magnesium atom?

A: 0

B: 12

C:24

D:36

Answer: The mass number of magnesium atom is 24 amu.

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 neutrons that are present in an atom. It is expressed in 'amu'

Mass number = Number of protons + Number of neutrons

For the given element, "magnesium"

Number of protons = 12

Number of neutrons = 12

Number of electrons = 12

Mass number = 12 + 12 = 24

Hence, the mass number of magnesium atom is 24 amu.

24, because to get the AMU of an element you just add the number of protons and neutrons, because of the fact that electrons weight next to nothing.