It’s water vapor, does this help?
The sodium ion becomes hydrated. when sodium chloride dissolves in water, the sodium and chloride ions and the polar water molecules are strongly attracted to one another by ion-dipole interactions
The reducing agent will itself be oxidized.
The oxidation number of carbon goes form 0 to +2. Therefore, it is the reducing agent.
It is B that one has the most mass
C: plates slipping along a fault