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Nucleus - the centre of atom made up of  proton and neutron this provides mass to the entire atom.
nucleons - the particles present inside the nucleus is known as the nucleons.

The outermost shell of an atom consisting of the valence electrons is valence shell.
Penultimate shell is the shell locate just before the valance shell..

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A nucleus is at the center of an atom, and it is that collection of particles, protons and neutrons, that make up the nucleus of that atom. Because atomic nuclei are composed of protons and neutrons, we have come up with the term nucleon to describe any particle that makes up an atomic nucleus. That means either a proton or a neutron, when we talk about them as part of the nucleus of an atom, can be properly called a nucleon. The nucleus of an atom is said to be made up of nucleons. 
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nucleus: centre of an atom which contain proton and neutron.
nucleons: nucleus contain which particle (neutron,proton) that particle called nucleons.
valance shell: on writing electronic configuration of an atom the last electron goes in which shell that orbital called valence shell.
penultimate shell: just before the valance shell.

  Na(11) = 2,8,1
valance shell = third
penultimate shell = second

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