What is the process in which small droplets collide and form larger drops called?

Correct answer: Collision and coalescence

Direct answer: A, collision and coalescence. Inside a cloud, air currents make small droplets move at different speeds and in different directions. When droplets meet, they collide; if they join to make one larger droplet, that joining is called coalescence. Repeated collision and coalescence can increase droplet size until the drops are heavy enough to fall as rain. A is correct because it names both stages of the process described. B is wrong because earthquakes and volcanoes are geological events, not droplet-growth processes. C is wrong because salinity concerns dissolved salts in water and tides concern the periodic movement of ocean water. D is wrong because weathering and erosion describe the breakdown and transport of rocks and soil. Memory cue: collision means ‘bump together’; coalescence means ‘join together.’ Together they help cloud droplets grow into raindrops.