The correct litmus test for an acid is:
yellow litmus turns blue
blue litmus turns red
red litmus turns yellow
o red litmus turns blue

The correct litmus test for an acid is:

blue litmus turns red

Explanation:

Litmus paper : It is a paper which contains 14 -15 dyes obtained  from Lichens

It is also called Acid-Base Indicator

It is used to test whether the given solution is acidic or not.

If the solution is acidic the litmus turns Red

If the solution is basic the litmus turns Blue

How to perform Litmus Test :

Place the drop of given solution over the litmus paper.

If the Litmus paper is Blue initially and On adding a drop of given solution , it turn red then it indicate that the solution is acid with pH = 3 to 7

Red litmus paper does not change its color if the solution is acidic .

If the Litmus paper is Red initially and On adding a drop of given solution , it turn Blue then it indicate that the solution is alkaline . pH= 4 to 12

Blue litmus does not change its color in the presence of alkaline solution.

blue litmus turns red

Explanation:

the correct litmus test for an acid is blue litmus turns red