Hint: Human cheek cells are skin cells, made up of epithelial cells. It is a type of eukaryotic cell lacking a cell wall and having negatively charged DNA and RNA. Thus, for staining the dye is of positive charge.
> Staining is the colouring of semi-transparent cells with dye. Staining can be performed by various stains. Stains can be divided into acidic and basic stains. Acidic stains are used to stain positively charged components like background e.g. nigrosin. Basic stains are used to stain negatively charged molecules such as nucleic acid e.g. methylene blue.
> Methylene blue is a positively charged molecule and stains negatively charged molecules as DNA and RNA inside cells. Cheek cells are epithelial cells which lack proteoglycans, proteins with basic amino acids. We can say that the correct answer is A as methylene blue
> Safranin is also basic dye and used majorly for bacteriological staining. It is used as a counter stain in bacterial staining. In human cells, safranin is used for staining of cartilage, mucin, and mast cell granules. The safranin binds with acidic proteoglycans in cartilage tissues with a high affinity forming a reddish orange complex.
> Acetocarmine is used to stain the chromosomes so that they can be easily visible. It is used to study cell mitosis. The chromosome numbers are also counted by using this at metaphase and anaphase. Thus acetocarmine is used for chromosome staining especially in onion cells.
> Eosin is xanthine dye which binds to compounds and forms salt with basic molecules like proteins containing amino acids such as arginine and lysine, and stains them dark red as a result of the actions of bromine on fluorescein. Eosin is used for staining of red blood cells, collagen, and muscle fibres.
Hence, The correct answer is option (A).
Note: Methylene blue is a type of basic dye, possesses positive charged molecules and stains negatively charged molecules as DNA and RNA inside cells. It is used to stain nucleic acid in cells which are negatively charged.