Question

Anything that influences the valence electrons will affect the chemistry of the element. Which one of the following factors does not affect the valence shell?
A.Valence principal quantum number $\,(n)\,$
B.Nuclear charge
C.Nuclear mass
D.Number of core electrons

Answer 1

Electrons are arranged in shells or orbitals in an atom. Valence electrons are often arranged in varying orbitals or shells that are often particles that are charged negatively. In addition , the interaction with atoms and the creation of chemical bonds was responsible for these electrons. Not all electrons, however, are connected with the molecule. In the forming of a chemical bond or a molecule, only the electrons found in the outermost shell will participate.

Complete step by step answer:
Principal quantum number(n) represents the number of orbits in an element. It is represented by letters $\,K,L,M,N\,$ equal to numbers $\,1,2,3,4\,$ and so on. The orbit closest to the nucleus is represented as $\,K\,$ and $\,n = 1\,$.The second orbit is represented as $\,L\,$ and $\,n = 2\,$, and so on. The closest orbit has lowest energy. The energy of an orbit increases with the increasing value of n.
Now what’s nuclear charge? It is the total charge in the nucleus for all the protons and this charge is positive, since proton is positively charged and as we all know, neutrons ( also present in nucleus) are uncharged particles. So neutrons do not contribute to the nuclear charge , but they do have mass so they contribute to the nuclear mass, which brings us to our next topic, that’s nuclear mass. It is the total mass of an atom that is the sum of the mass of protons and neutrons. Electrons have negligible mass.
Now we have one more term, what’s meant by the number of core electrons? The electrons in the valence shell that is the outermost shell are known as valence electrons. All the other electrons are called core electrons. These electrons do not participate in chemical reactions.
Now let’s come to the main question. Which factors do not affect the valence shell? Now I can easily just give you the answer, but it's necessary for you to understand WHY? More is the principal quantum number, more is the number of orbits, then the valence shell is getting farther from the nucleus. Farther the valence shell is the reactivity. So we can conclude that the valence shell depends on the principal quantum number.
Now, more is the nuclear charge greater will be the pull of the outermost orbit or valence shell towards the nucleus, so the radius decreases and reactivity also decreases. So, valence shells also depend on nuclear charge.
Now, the more the number of core electrons, more are the number of core electron shells, larger is the size of the atom and farther is the valence shell of the atom, thus making it more reactive. So, the valence shell depends on the number of core electrons too.
Nuclear mass as I explained earlier is the total mass of protons and neutrons and mass has nothing to do with reactivity and it does not affect the valence shell. Protons (nuclear charge) affect the valence shell but neutrons do not as neutrons are uncharged.
So, the correct answer is option C) Nuclear Mass.

Note: All the trends in periodic tables are a must learn thing if you want to answer questions like these with accuracy. Here are a few important trends which should be remembered .
-Atomic radius increases down the group.
-Ionization enthalpy ,electron affinity and electronegativity increases across the period from left to right.
-Metallic character increases down the group.