Best choice to demonstrate only DNA | MDS entrance preaparations

Which of the following reactions is the best choice to demonstrate only DNA? 
A. Gallocyanin-chrome alum method.
B. Feulgen reaction.
C. Solo chrome cyanine method.
D. Thioflavine S stain

. Ans. B. Feulgen reaction.

Gallocyanin-chrome alum method will stain both DNA and RNA dark blue and,    therefore, cannot provide a good estimate on the amount of DNA in the cell. Thioflavine S stain can be used to demonstrate amyloid deposition and must be visualized with a fluorescent microscope. It cannot be used to estimate the amount of DNA in tissue sections. Solo chrome cyanine method can be used to differentiate osteoid from newly laid-down bone and older bone but does not stain DNA specifically. Feulgen reaction stains DNA red-purple and the cytoplasm green and is a widely accepted method to demonstrate DNA on histologic sections.