Answer:
a) 
b) 
c) 
Explanation:
Hello,
In this case, in each reaction we must subtract the Gibbs free energy of formation the reactants to the Gibbs free energy of formation of the products considering each species stoichiometric coefficients. In such a way, the Gibbs free energy of formations are:

So we proceed as follows:
a)

b)

c)

Regards.
Answer:
They aren't listed as a whole number, because an atom's mass is not always a whole number. The mass differs between types of atoms as well.
Answer:
The 4s2 is preventing 3d10 from following 1s2 2s2 2p6 3s2 3p6.
Explanation:
the meme is quite common.