(c) There is no change in the blue litmus paper and the red litmus paper turns blue.
Saponification which basically refers to the reaction between metallic alkali and a fat or oil to produce soap. It involves the hydrolysis of an ester under acidic or basic conditions and results in the formation of an alcohol and a salt of carboxylic acid.
We also know that the litmus paper is a kind of filter paper which is treated with water soluble dye and it can be used as a pH indicator. So, under basic conditions, the red litmus paper turns blue and under acidic conditions, blue litmus paper turns red.
Soaps are slightly basic because they are the salts of strong bases and weak acids.
Base does not affect blue litmus because it doesn’t consist of acidic ions which can turn blue litmus red.