Here it says which of the following processes represents an endothermic reaction. Remember, endothermic reactions are heat absorbing, bond breaking reactions. So here we have steam condensing. If you're condensing, you're going from a gas to a liquid. Here you're not breaking bonds, you're forming them. So this is out.
Next, molten lava solidifying. Solidifying means you're going from a liquid to a solid. Again, you're not breaking bonds. Water boiling. If you're boiling, that means you're vaporizing your liquid water into a gas. You're breaking bonds here, so this is endothermic.
And then finally we have water freezing. If you're freezing, you're going from the liquid phase to the well. Actually, you're going from, yes, the liquid phase to the solid phase. Here you're not breaking bonds, you're forming them. So this would not be endothermic. So out of all the options, only option C represents an endothermic reaction.