How does force of gravity on raindrop compare with air drag it encounters when it falls at constant velocity? Will it be force of gravity is larger/smaller/equal to force of air drag

Think about Newton's law: F= ma. This says that if an object has a net force on it, it accelerates. Conversely, if there is no net force the object's acceleration is 0, which means its velocity is constant, as is the case with your raindrop. So the raindrop feels a down force of its weight, and an up force from air resistance - what must the net force be for it to have constant velocity?