An atom is neutral because it contains an equal number of protons and electrons. Though the atom actually contains neutrons, this reason does not explain the electrical neutrality of the atom.
The L shell actually contains eight electrons because the maximum number of electrons accommodated in each shell is given by 2n^2 where n is the principal quantum number. Since the L-shell corresponds to n=2 then the reason is the correct explanation of the assertion.
The valency of atoms is determined by the number of electrons in the outermost shell of the atom. Remember that atoms having a filed valence shell(eight electrons in the outermost shell) have a valency of zero. Hence the noble gases possess a zero valency. Thus the reason is the correct explanation of the assertion.
Nitrogen forms its ion by electron gain and not by electron loss because nitrogen forms an anion. This anion is formed by a gain of three electrons. The assertion is false but the reason is true.
