The phenomenon that shows that increase in pressure lowers the melting point can be observed in

Analyze the question: The question asks which phenomenon demonstrates that higher pressure lowers the melting point of a substance (specifically ice).

Explain the concept: Ice is unusual because it is less dense than liquid water. When pressure is applied to ice, the ice tends to melt into the denser water, so the melting point drops below 0°C. When the pressure is removed, the water refreezes. This melting under pressure followed by refreezing when the pressure is released is called regelation.

Check each option:

• A. Sublimation: A solid changes directly into a gas without becoming liquid. It has nothing to do with pressure lowering the melting point.
• B. Condensation: A gas changes to a liquid. This is not related to melting.
• C. Coagulation: The clumping or clotting of particles, as in blood or colloids. It is not a melting phenomenon.
• D. Regelation: Ice melts under pressure and refreezes when the pressure is removed. This matches the question.

Classic example: If you hang a thin wire over a block of ice with a heavy weight on each end, the wire slowly cuts through the ice. The high pressure beneath the wire lowers the melting point, so the ice melts. The water then flows above the wire, where the pressure is normal, and refreezes. The block stays in one piece even though the wire passes through it. Ice skating and the movement of glaciers are other examples.

Answer: D. Regelation.

Exam tip: "Regelation" means "freezing again" (re- + gelare, "to freeze"). Whenever you see "pressure lowers melting point," think of ice, the wire-and-weights experiment, and regelation.