In the formation of a primary rainbow, there are two internal reflections of light that take place. When sunlight passes through a raindrop and hits the inner surface of the drop, it undergoes the first internal reflection. This causes the light to change direction and separate into its different colors due to the phenomenon of dispersion.

After the first reflection, the light continues to travel within the raindrop and reaches the other side, where it undergoes a second internal reflection at the outer surface of the drop. This second reflection causes the light to change direction once again and exit the raindrop.

Upon exiting the raindrop, the light continues to disperse further and forms a circular arc of colors in the sky, creating a primary rainbow. The specific angle at which the light enters and exits the raindrop determines the size and position of the rainbow.

Therefore, the correct answer is 2, indicating that two internal reflections occur in the formation of a primary rainbow.