Select the most appropriate meaning of the given Idiom:-

An acid test 

A critical test

The most appropriate meaning of the idiom "an acid test" is a critical test. The idiom comes from the fact that acid is a strong substance that can dissolve or destroy other substances. In this sense, an acid test is a test that is so difficult or challenging that it will reveal the true nature of something.

The other options are not as accurate descriptions of the meaning of the idiom. Pouring acid on something is not a common expression for a critical test. To take an important part is not the same as a critical test. Suspect something foul is not typically associated with the idiom "an acid test."