Final answer:
When using red litmus paper, a color change would occur with a base or alkaline substance such as soap, lemon juice, or antifreeze, but not with vinegar.
Step-by-step explanation:
pH testing with litmus paper involves using paper strips impregnated with natural dyes extracted from lichens. When dipped into a solution, the paper changes color based on the solution's acidity or alkalinity. Blue litmus paper turns red under acidic conditions, while red litmus paper turns blue under alkaline conditions.
When using red litmus paper to test the pH value of different solutions, the litmus paper would change color when it comes into contact with a base or an alkaline substance. Soap, lemon juice, and antifreeze are examples of bases, while vinegar is an acidic substance that would not result in a color change of the litmus paper.