(A.) Nickel and oxygen reacting chemically could create a compound. (Most likely some sort of oxide)
The pure silver is only made up of one element, so it can't be a compound.
The sandwich and all it's components may contain chemical compounds, but is not a compound in itself.
While it is possible that the material the nails are made out of is a compound, we are not given this information. Simply stating that nails (no matter the size) are in a box, does not make it a compound.
