I might need a diagram for this, but I have a vague idea of what you are talking about.
If H20 is going left it means the temperature is going lower.
The molecules will condense to slowly become ice
7.8 g/cm3 because Mass/Volume=Density
C. The number of neutrons
Since Carbon 12 has 6 neutrons
And carbon 13 has 7 neutrons.
You know that elements have equal protons (atomic number) and electrons