To solve this problem, we need to analyze the formation of rainbows and identify the incorrect statement.$\\$Let's evaluate each option:$\\$• Option 1: $$When light rays undergo two internal reflections in a water drop, a secondary rainbow is formed.$\\$This statement is correct. A secondary rainbow is indeed formed due to two internal reflections within the water droplets.$\\$• Option 2: $$The order of colours is reversed in the secondary rainbow.$\\$This statement is correct. In a secondary rainbow, the order of colors is reversed compared to the primary rainbow.$\\$• Option 3: $$An observer can see a rainbow when his front is towards the sun.$\\$This statement is incorrect. To see a rainbow, the observer must have their back to the sun, with the sunlight entering the raindrops in front of them.$\\$• Option 4: $$Rainbow is a combined effect of dispersion, refraction, and reflection of sunlight.$\\$This statement is correct. The formation of a rainbow involves the dispersion, refraction, and reflection of sunlight within raindrops.$\\$Therefore, the incorrect statement is Option 3.$\\$The correct answer is Option 3.