Recessive dystrophic epidermolysis Bullosa occurs due to alteration in:: (A) Type 4 collagen, (B) Type 6 collagen, (C) Type 7 collagen, (D) Type 8 collagen
Answer is C. "Nikolsky's sign" is positive in: 

Pemphigus
Familial benign chronic pemphigus (hailey-hailey disease)
Recessive dystrophic epidermolvsis bullosa [Epidermolysis bullosa occurs due to alteration in structure of type VII  collagen.