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which of the diagrams is the correct model for the element beryllium?

#12

B is the correct model of beryllium.

Explanation:

An atom consist of electron, protons and neutrons. Protons and neutrons are present with in nucleus while the electrons are present out side the nucleus.

All these three subatomic particles construct an atom. A neutral atom have equal number of proton and electron. In other words we can say that negative and positive charges are equal in magnitude and cancel the each other. For example if neutral atom has 6 protons than it must have 6 electrons. The sum of neutrons and protons is the mass number of an atom while the number of protons are number of electrons is the atomic number of an atom.

For example  in case of beryllium:

The atomic number of beryllium is 4.

The atomic mass is 9 amu.

Number protons = 4

Number of electrons = 4

Number of neutrons = 9-4 = 5

So b is correct answer because 5 neutrons and 4 protons are present with in nucleus while 4 electrons are present out side.