As the Earth , heavier elements such as and nickel moved to the center of the Earth. This was the beginning of the layers of the Earth with the outer layer being covering the magma?

The Four Layers

Many geologists believe that as the Earth cooled the heavier, denser materials sank to the center and the lighter materials rose to the top. Because of this, the crust is made of the lightest materials (rock- basalts and granites) and the core consists of heavy metals (nickel and iron).

Here we have to find the diameter of nucleus as the diameter of atom is given.
Diameter of atom is 1 x 10⁻⁸ cm
Radius of atom = diameter/2
so, radius of atom = 1 x 10⁻⁸ cm/2 = 5 x 10⁻⁹ cm
To find diameter of nucleus, first we have to find the radius of nucleus by using this formula,
R = rA⁽¹/³⁾     where R = radius of nucleus, r = radius of atom and A is a nucleon number, which is different for every atom
so, R=(5x10⁻⁹)A⁽¹/³⁾  
here atom is not mentioned, so we don't know the value of A
and Dimeter (D) = 2R, R = D/2
 D/2 = (5x10⁻⁹)A⁽¹/³⁾
Diameter of nucleus (D) = 2((5x10⁻⁹)A⁽¹/³⁾)