The correct option is
B more
The given sentence consists of a comparison between two things.
In a comparison sentence that consists of two clauses, both must be parallel in structure.
Option A: 'More' placed before an adjective makes it a comparative adjective. Since the first half of the sentence contains the words 'more the air', the second half of the sentence will also begin with 'more': 'the more slowly the satellite will travel'.
Hence option A is correct.
Option B: 'Less' is the opposite of 'more'. It means 'to a smaller extent, amount or degree'. It does not form a parallel structure in the given sentence.
Option C: 'Very' means 'extremely, to a high degree'. It does not form a parallel structure. 'The very slowly' sounds ambiguous in meaning.
Option D: 'Much' expresses a large amount of something, and functions as an intensifier. But, 'much' does not put an adjective in comparative degree. The sentence being in comparison, 'much' is not parallel in structure to 'the more air'.
Hence options B, C and D are incorrect.