1. Recall how a primary rainbow is formed

A primary rainbow is formed when sunlight enters a raindrop, gets refracted, then undergoes one internal reflection, and finally refracts again while emerging.

So for a primary rainbow:

• number of internal reflections $=1$
• it is usually brighter than the secondary rainbow

2. Order of colours in a primary rainbow

Due to dispersion, different colours emerge at slightly different angles:

• Red light emerges at a larger angle
• Violet light emerges at a smaller angle

Hence, in the sky for a primary rainbow:

• red appears on the outer/top side
• violet appears on the inner/bottom side

So the observer sees: $\text{Red on top, violet on bottom}$

3. Check each option

Option A

In primary rainbow, observer sees red colour on the top and violet on the bottom

This is correct.

Option B

In primary rainbow, observer sees violet colour on the top and red on the bottom

This is the reverse order, so it is incorrect.

Option C

In primary rainbow, light wave suffers total internal reflection twice before coming out of water drops.

A primary rainbow is formed after one internal reflection, not two. Two internal reflections correspond to a secondary rainbow. Hence this is incorrect.

Option D

Primary rainbow is less bright than secondary rainbow.

Actually, the primary rainbow is brighter than the secondary rainbow because fewer reflections mean less light loss. So this is incorrect.

4. Final answer

Only Option A is correct.

$\boxed{A}$

5. Comparison with stored correct answer

Stored correct answer = A

My derived answer = A

They match.