1, 2, 4, 8, 16, 32, 64, 128, 256
The orange vendor can ask for only 1 orange, so one box must contain 1 orange.
He can ask for 2 oranges, so one box must contain 2 oranges.
He can ask for 3 oranges, in that case box one and box two will add up to 3.
He can ask for 4 oranges, so one box i.e. third box must contain 4 oranges.
Now using box number one, two and three containing 1, 2 and 4 oranges respectively, his son can give upto 7 oranges.Hence, forth box must contain 8 oranges.
Similarly, using first four boxes containing 1, 2, 4 and 8 oranges, his son can give upto 15 oranges. Hence fifth box must contain 16 oranges.
You must have noticed one thing till now that each box till now contains power of 2 oranges. Hence the answer is 1,2, 4, 8, 16, 32, 64, 128, 256. This is true for any number of oranges, here in our case only upto 511.