When a small raindrop falls through air, it initially experiences an upward force due to air resistance. As a result, the raindrop accelerates downwards. However, as the raindrop picks up speed, the air resistance acting on it also increases. Eventually, a point is reached where the force due to air resistance is equal to the weight of the raindrop. At this point, the net force on the raindrop becomes zero, and it reaches its terminal velocity.

Option 1 is incorrect because the raindrop`s velocity does not continue to increase indefinitely. Once the raindrop reaches its terminal velocity, it will no longer accelerate.

Option 2 is incorrect because the raindrop`s velocity does not continue to decrease. Instead, it reaches a point where it becomes constant.

Option 3 is the correct answer. The raindrop`s velocity increases for some time as it accelerates due to gravity, but it eventually becomes constant when the force due to air resistance equals the weight of the raindrop.

Option 4 is incorrect because the raindrop does not fall with a constant speed initially. It only reaches a constant speed after accelerating for some time.