The air is at room temperature and has an amount of water evaporated and dissolved in the air. When ice water is poured into a glass, the wall of the glass will cool to the temperature of the ice water. When the air comes into contact with the frozen glass, the gaseous water dissolved in the air will lower its temperature, thus the energy will decrease and the water will condense, making the outside of the glass wet.
Therefore, we can complete the sentence as follows:
The water molecules in the air will condense on the cold beaker because they decresases the energy and move slower.