Notice that the correct answer, A, is a precisely parallel construction. The logical structure is: If thunder is the atmosphere's most noisy production then lightning is the atmosphere's most dazzling production. We can change "most noisy" to "noisiest" because it's shorter. We can't change "most dazzling" to "dazzlingest" because there is no such word. We can leave out the word "then," because in be inferred from context. We can replace the second occurrence "the atmosphere's" with "its" to save time and repetition. We can leave out the second occurrence of "production," because it can be inferred from context.

"If thunder IS..." - you have a present-tense verb here, so the missing part must also have a present tense verb. Simple.

If thunder is the atmosphere's noisiest production, lightning IS CERTAINLY (A) its most dazzling.

definitely A