Option 1 -> "ingenuous" means innocent or naive, which doesn't describe skill at puzzles.
Option 2 -> "ingenious" means clever, inventive, and skillful—perfect for describing someone good at crosswords.
Option 3 -> "inherent" means inborn or natural quality, but doesn't work with "at solving" grammatically.
Option 4 -> "inimical" means harmful or hostile, which is completely opposite to the intended meaning.
Hence, Option 2: ingenious -> The sentence describes Ravi's cleverness and skill at solving difficult crossword puzzles, which requires ingenuity and creative problem-solving abilities -> correct