D. 8! 7! 6! 2!
Feedback Here volumes of the same book are not to be separated i.e. all the volumes of the same book are to be kept together. Regarding all volumes of the same book as one book, we have only 4 + 1 + 1 + 1 = 7 books. These 7 books can be arranged in 7! ways. Volumes of book having 6 volumes can be arranged in 6! ways. Volumes of book having 8 volumes can be arranged in 8! ways.
Volumes of book having 2 volumes can be arranged in 2! ways.
∴ Required number = 7! 8! 6! 2!.