Which of the following is a process with a negative ΔS?

a) CaCO3 (s) → CaO (s) + CO2 (g)

b) CO2 (s) → CO2 (g)

c) None of the choices are correct because ΔS cannot be negative.

d) dissolving sugar in water

e) H2O (l) → H2 (s)

The only reaction there that has a negative delta S is H2O (l) going to H2 (s). That is because liquids have more entropy than solids therefore the change is negative since you are going from a higher state of entropy to a lower state of entropy. However, I don't know if that reaction is possible. For one, the oxygen disappears and two, liquid hydrogen is really hard to make. I don't think a reaction can produce it.