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

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.

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.