Which substance will cause litmus paper to turn red?

acidic substances, for example lemon juice

Litmus paper-" A tool or system to measure a substance characteristics regarding there pH. As to check whether they are acidic, basic or neutral in nature."

A certain paper which is termed as litmus paper is stained with litmus, and then a certain substance which is under observation is stained over it. And then its properties are measured. The standard provided to us shows us that pH recorded lower then 7 is acidic in nature, leveled at 7 is neutral and higher then 7 is termed as a basic substance.

Explanation:

Now, if the if the substance stained on a blue litmus paper is acidic then it turns in to red. And if its a basic or alkaline substance then the red litmus paper is turned blue.