Explain why adding ice to a hot drink lowers the tempature

Because ice molecules move slowly and cluster tightly together, they produce a low amount of heat. In other words, ice absorbs heat from the water. As the water molecules lose energy because of it's absorbed molecules, they begin to slow down, causing the water to cool.

When heat transfers from your beverage to the ice and the temperature of the liquid drops, the molecules in the beverage slow down.