Western blot technique is done for-: (A) Mitochondiral RNA, (B) Double strand DNA, (C) r-RNA, (D) Protein
Answer is D. Visualization of a specific DNA or RNA fragment among the many thousand of contaminating molecules requires the convergence of a number of techniques collectively termed the blot transfer.

Southern blot → Detects DNA
Northern blot → Detects RNA
Western blot → Detects proteins (proteins are separated by electrophoresis, renatured and analysed for an interaction by hybridization with a specific labelled DNA probe).