Which of the following is NOT commonly used for stain removal?

Cola is the answer because it is not commonly recognized or recommended for stain removal purposes like the other options. Instead, vinegar is often praised for its acidity, which helps break down stains, especially those from organic materials. Club soda and clear soda are also popular for their effervescent properties, which can lift stains, particularly those from fabrics and carpets. Cola, on the other hand, is sugary and may leave a residue that can actually attract more dirt, potentially making stains worse. This characteristic makes it less suitable for stain removal compared to the other listed options, which have established reputations for their effectiveness in tackling various types of stains.