Which of the following statement is correct?

We need to identify the correct statement about a primary rainbow.

Option A: In primary rainbow, observer sees red colour on the top and violet on the bottom.

In a primary rainbow, sunlight enters a water droplet, undergoes one internal reflection, and exits. The red light is deviated less than violet light. Due to the geometry of the rainbow formation, the red arc appears on the outer (top) edge and the violet arc appears on the inner (bottom) edge. This is correct.

Option B: Violet on top and red on bottom.

This describes a secondary rainbow, not a primary one. This is incorrect.

Option C: Light suffers total internal reflection twice.

In a primary rainbow, light undergoes one internal reflection (not total internal reflection). Total internal reflection would not allow light to exit the drop. This is incorrect.

Option D: Primary rainbow is less bright than secondary rainbow.

The primary rainbow is brighter than the secondary rainbow because the secondary involves an additional reflection, losing more light intensity. This is incorrect.

Hence, the correct answer is Option A.