Litmus paper is a paper that is used to identify whether a solution is acidic or basic.
litmus paper is of two types:
red litmus and blue litmus
If we dip red litmus on acid its color remains unchanged.
If we dip red litmus on basic solution, the paper turns blue.
If we dip Blue litmus on acid solution, the paper turns red.
If we dip blue litmus on basic solution, the color remains unchanged.