$$\begin{array}{|l|l|l|}\hline {\text { Substance }} & \text { Action on Litmus paper } & \text { Red Litmus paper } \\\hline \text { Dry HCl gas } & \text { None } & \text { None } \\\hline \text { Moistened } \mathrm{NH}_{3} & \text { None } & \text { Turns blue } \\\hline \text { Lemon juice } & \text { Turns red } & \text { None } \\\hline \text { Carbonated soft drink } & \text { None } & \text { Turns blue } \\\hline \text { Curd } & \text { Turns red } & \text { None } \\\hline \text { Soap solution } & \text { None } & \text { Turns blue } \\\hline\end{array}$$